One of the biggest running gags on social media and Reddit is how hot and power hungry CPUs have become over the years. Whereas at one time flagship x86 CPUs didn't even require a heatsink, they can now saturate whole radiators. Thankfully, it's not quite to the levels of a nuclear reactor, as the memes go – but as the kids say these days, it's also not a nothingburger. Designing for higher TDPs and greater power consumption has allowed chipmakers to keep pushing the envelope in terms of performance – something that's no easy feat in a post-Dennard world – but it's certainly created some new headaches regarding power consumption and heat in the process. Something that, for better or worse, the latest flagship chips from both AMD and Intel exemplify.

But despite these general trends, this doesn't mean that a high performance desktop CPU also needs to be a power hog. In our review of AMD's Ryzen 9 7950X, our testing showed that even capped at a these days pedestrian 65 Watts, the 7950X could deliver a significant amount of performance at less than half its normal power consumption.

If you'll pardon the pun, power efficiency has become a hot talking point these days, as enthusiasts look to save on their energy bills (especially in Europe) while still enjoying fast CPU performance, looking for other ways to take advantage of the full silicon capabilities of AMD's Raphael and Intel's Raptor Lake-S platforms besides stuffing the chips with as many joules as possible. All the while, the small form factor market remains a steadfast outpost for high efficiency chips, where cooler chips are critical for building smaller and more compact systems that can forego the need for large cooling systems.

All of this is to say that while it's great to see the envelope pushed in terms of peak performance, the typical focus on how an unlocked chip scales when overclocking (pushing CPU frequency and CPU VCore voltages) is just one way to look at overall CPU performance. So today we are going to go the other way, and to take a look at overall energy efficiency for users – to see what happens when we aim for the sweet spot on the voltage/frequency curve. To that end, today we're investigating how the Intel Core i9-13900K and AMD Ryzen 9 7950X perform at different power levels, and to see what kind of benefits power scaling can provide compared to stock settings.

The Ever Changing Definition of TDP (Thermal Design Power)

One of the most frustrating talking points surrounding processors involves TDP, or more specifically, what TDP even is. While the term has a fixed definition – Thermal Design Power – what that actually means in regards to the specifications of a product varies from one hardware maker to the next. Even Intel and AMD have slightly different definitions of TDP (despite sharing the x86 CPU market), which makes it a complicated and at-times confusing term. In short, TDP is no longer an unflinching guide to the maximum power consumption from a specific processor – or even how much heat energy can dissipate from a processor

This is is a matter we have given plenty of column inches to over the years, so below are some previous articles on the subject of power and TDP:

• Why Intel Processors Draw More Power Than Expected: TDP and Turbo Explained
• Talking TDP, Turbo, and Overclocking: An Interview with Intel Fellow Guy Therien

Starting with Intel, while the company assigns official TDP figures to its processors, the reality is that their unlocked processors are not limited to one assigned power figure. At best, Intel offers a set of TDP values based around the base frequency of their chips, while power level 1 (PL1) and power level 2 (PL2) ratings are laid on top of that to define the power parameters for those all-important (and all-advertised) turbo clock speeds.

Meanwhile, looking at how AMD defines its TDP figures has been made more difficult with the release of its Ryzen 7000 series processors and the accompanying AM5 platform. While AMD does give out default TDP figures the Ryzen 7000 series, this is no more a hard ceiling than it is with Intel; the other element is what AMD calls Package Power Tracking, or PPT for short. The defined TDP value is assigned to its processors based on default frequency levels, while PPT is defined as the limitation to what the actual socket can deliver in terms of power (and what flagship chips tuned for maximum performance will try to consume).

The long and short of matters is that, on practically any consumer-level motherboard paired with an adequate cooler, using any unlocked processor, including the two we're focusing on today, will circumvent the chip's base TDP rating in order to provide the highest turbo clock speeds possible, capped only by the temperature and electrical delivery limits. So taking the Ryzen 9 7950X as an example, although the default TDP is 170 W, the actual PPT wattage is defined as 230 W (with a sustained current of 160 A).

The good news, however, is that these power limits are easily user-adjustable on both AMD and Intel platforms. Many motherboards for both platforms offer a plethora of adjustable values to raise and lower these limits, and even within Windows there are software packages like AMD's Ryzen Master and Intel's XTU that can make the necessary changes.

Finding The Sweet Spot Balance Between Performance, Power, and Heat

For its latest series of processors, AMD is offering a new feature called ECO Mode, which reduces a 170 W TDP-rated processor to 105 W (and a 105 W TDP-rated processor down to 65 W). When we reviewed the AMD Ryzen 9 7950X processor, we found some interesting results when using it at 65 W instead of its default value of 170 W.

The most important thing we observed was that at 65 W, the Ryzen 9 7950X processor outperformed the Intel Core i9-12900K at default settings in the CineBench R23 multi-threaded test, which is nothing short of impressive. Since then, Intel released its 13th Gen Core series codenamed Raptor Lake, so the overall playing field has been leveled some. But still, it shows the potential value in dialing down the power consumption of a flagship CPU, as the 7950X was able to deliver 80% of its peak performance at under half the power consumption.

Those findings, in turn, inspired the thesis behind this doing this article: we wondered how both the Core i9-13900K and Ryzen 9 7950X performed when using it with various power restrictions applied. So for this article, we're going ahead and testing just that situation, running AMD and Intel's flagship CPUs are various power levels.

We've selected several power limits/PPTs to test, including the following:

• Intel Core i9-13900K at default settings (125 W base, 253 W turbo)
• AMD Ryzen 9 7950X at default settings (170 W base, 230 W PPT)
• Both at 125 W
• Both at 105 W
• Both at 65 W
• Both at 35 W

Throughout all of this, it's important to note that the Intel Core i9-13900K and AMD Ryzen 9 7950X have a critical distinction in terms of construction: chiplets. Whereas the Core i9-13900K is a monolithic design with cache, core, memory controller (IMC), and iGPU all being built within a single die, AMD's Ryzen 9 7950X is built upon a chiplet design. As a result, the 7950X uses three different chiplets for all of its major functions, with two eight-core core complex dies (CCD) and one IO die (IOD) containing the memory controller, PCIe, and graphics.

A screenshot from AMD's Ryzen Master Overclocking software during testing

This means that when setting a defined power limited with the Core i9-13900K, it's limiting power from all of the variables as mentioned. Whereas doing the same on the Ryzen 9 7950X wouldn't yield the quite same effect, as the IOD and CCDs operate semi-independently, albeit through AMD's Infinity Fabric interconnect. To properly limit the power on the Ryzen 9 7950X, the Package Power Tracking limit would need to be applied to constrict the power limits properly, such as setting a value of 125 W on the PPT and not just on the CPU cores.

Test Bed and Setup

Since both Intel and AMD use different platforms and sockets, we're using the MSI MPG Z790 Carbon WIFI for the Core i9-13900K and the GIGABYTE X670E Aorus Master for the Ryzen 9 7950X. To try and keep things on a level playing field, we're using an SK Hynix Platinum P41 2TB NVMe storage drive and AMD Radeon RX 6950 XT graphics card.

Normally we would rely on JEDEC memory settings defined by each platform, but in this case, we've opted to test both platforms with the same SK Hynix DDR5-5600B CL46 memory configuration. This is the memory we used for the Intel Core i9-13900K review, but it's faster than the highest official JEDEC settings supported by AMD's Ryzen 7000 series platform (DDR5-5200). Either way, we wanted to make our comparisons as apples-to-apples as possible, including holding memory at a constant performance and power level to investigate the benefits (if any) of restricting system power draw.

Power Scaling Test Bed (DDR5) Intel & AMD
CPUs	Core i9-13900K ($589) 24 Cores, 32 Threads 125 W Base, 253 W Turbo Ryzen 9 7950X ($699) 16 Cores, 32 Threads 170 W Base, 230 W PPT
Motherboards	MSI MPG Z790 Carbon WIFI (13900K) GIGABYTE X670E Aorus Master (7950X)
Memory	SK Hynix 2x16 GB DDR5-5600B CL46
Cooling	EKWB EK-AIO Elite 360 D-RGB 360mm
Storage	SK Hynix Platinum P41 2TB PCIe 4.0 x4
Power Supply	Corsair HX1000
GPUs	AMD Radeon RX 6950 XT, 31.0.12019
Operating Systems	Windows 11 22H2

Regarding benchmarks, we've opted for a small selection of rendering and encoding tests as we believe these will highlight differences in processor performance at the different power levels. For gaming, we've opted for Total War: Warhammer 3, as this is a notoriously heavily CPU-dependent title, while Borderlands 3 is more graphically demanding. We thought it would be prudent to test one of each, although if anyone would like to request more titles from our CPU 2023 benchmarking suite, feel free, and we'll add data as we find the time to collect and collate it.

Core i9-13900K & Ryzen 9 7950X Scaling Performance: CPU Short Form

For the compute side of our testing to determine how well the Core i9-13900K and Ryzen 9 7950X scale at different power levels, we've opted for a range of CPU-intensive benchmarks, particularly from the rendering and encoding section of our test suite.

To keep the playing field even, we are using the same SK Hynix DDR5-5600B 2 x 16 GB memory kit throughout all of our testing. We've separated the results within the same graph to outlay performance differences at different power levels so that users can see the differences and comparison in performance on offer from both the Core i9-13900K and Ryzen 9 7950X processors.

CineBench R23: Single and Multi-Threaded Performance

Focusing on performance in CineBench, it is worth highlighting that in the single-threaded test, Intel's Core i9-13900K displayed better single-core performance throughout. It didn't impact single-threaded performance on either processor despite restricting the power levels, which is exactly what we'd expect to find. While highly clocked CPU cores are very expensive from a power perspective, they are not so expensive as to consume the complete power budget of chips such as these.

Looking at multi-threaded performance in CineBench R23, this is where restricting the power levels makes the difference. Although Intel has the best performance in CineBench R23 MT at stock settings, it's AMD that scales better (i.e. loses less performance) as the power is restricted. Even at 65 W, the Ryzen 9 7950X is faster than the Core i9-13900 at 125 W, which is very impressive. Both processors take a massive hit in performance at 35 W, which is to be expected as we're now some 200 Watts below their stock power limits.

C-Ray 1.2: 4K, 16 Rays Per Pixel

Looking at the results in our C-Ray benchmark, the results between stock settings to 65 W impacted our figures. Starting with the Ryzen 9 7950X, there was a marginal performance loss between stock settings at 125 W and 105 W. Going from stock settings to 65 W (2.5X power), there was a drop in C-Ray performance of around 16%.

Focusing on the Core i9-13900K, its performance was heavily power reliant when comparing stock settings to 125 W, 105 W, and 65 W. Even from stock settings to 125 W, there's a performance loss of around 21%, and even more so comparing stock settings to 65 W, which equates to around 38%.

Things tailed off massively when both set to 35 W, with the AMD Ryzen 9 7950X beating the Intel Core i9-13900K convincingly here.

POV-Ray 3.7.1: 

In our POV-Ray benchmark, we saw some interesting behavior. Although the Core i9-13900K at default settings comfortably beat the Ryzen 9 7950X, the 7950X held its performance well when dropping down the power, with the 7950X's result at 65 W being similar to the 13900K at 105 W. This shows that the Ryzen 9 7950X and its 5 nm die is more scalable at lower power.

Blender 3.4: CPU Only Compute

At default settings, the Core i9-13900K and Ryzen 9 7950X was competitive in all of the Blender sub-tests, even when restricting the power. Once power was restricted, we saw that the 7950X held onto much of its performance, while the 13900K didn't fare so well. In the Fishy Cat subtest at 65 W, the 7950X was 62% faster than the 13900K, which is impressive scaling here by AMD.

x264 Encoding: 1080p and 4K Bosphorus

The x264 benchmark focuses on encoding performance, and at default settings, AMD's Ryzen 9 7950X wins out. Even dropping down to 125 W, the 7950X only loses around 2% at 1080p and around 4% at 105 W. At 65 W, the 7950X is around 16% slower than at default settings.

Looking at Intel's Core i9-13900K, the 13900K loses around 15% performance by restricting power to 125 W compared to default settings. This is another example that the 5 nm Zen 4 architecture scales much better at lower power envelopes than Intel's 10 nm refresh; this isn't unexpected, however.

Core i9-13900K & Ryzen 9 7950X Scaling Performance: Peak Power/Temps & Gaming

In our gaming performance testing, we're using two very different titles to measure any gains (if any) when dropping the power on the Core i9-13900K and Ryzen 9 7950X. The first title is Total War: Warhammer 3, which is notoriously hungry in terms of processor performance. We felt this would be a good measuring stick to see how performance stands as we restrict power to the processor. The second title is Borderlands 3, which albeit more graphically intensive than TW: Warhammer 3, still benefits from processing power as many other titles do.

We'll first go over the peak package power and core temperatures.

Peak Power and Core Temperature: Feat yCruncher and AIDA64

One of the main benefits of reducing power consumption and electrical load on a component is temperature; less power means less heat. As we reduce the TDP and test with power restrictions, we should also see a noticeable reduction in heat and CPU core temperatures. To measure the peak package power load from the CPU and to determine the peak core temperatures, we are using AIDA64 to record both variables. Putting full load on the CPU is yCruncher, which we use to measure peak processor package power in our CPU reviews.

Starting with the peak power figures, it's worth noting that AMD's figures can be wide off the mark even when restricting the Package Power Tracking (PPT) in the firmware. For example, restricting the socket and 7950X to 125 W yielded a measured power consumption that was still a whopping 33% higher. By comparison, the 13900K exceeded its set limits by around 14% under full load. In all cases though, this is still a significant power reduction versus their stock settings, especially in the case of the power-hungry i9-13900K.

Following on from the temperatures, despite pulling a figure of 330.3 W under full load, the peak core temperature of the i9-1300K was 8°C lower than the Ryzen 9 7950X, which hit 94°C under full load. Given that the power figures given aligned more with the settings on the 13900K than they did on the 7950X, the drop in temperatures on the Intel processor was much better received, with 53°C at 125 W and just 39°C at 65 W.

There's certainly more performance at 65 W from our compute testing on the Ryzen 9 7950X, but it's drawing more power than it should be. It's also running hotter despite using a premium 360mm AIO CPU cooler, which is more than enough even at full load. As a reference, the room that all the testing was done at ranged between 22 and 24°C, so this shouldn't impact any of our thermal results too much.

Total War: Warhammer 3: 1080p Ultra and 4K Medium Settings

In Total War: Warhammer 3, we saw something very interesting. Dropping the power on the AMD Ryzen 9 7950X, even down to just 35 W, didn't seem to impact performance at either 1080p Ultra or 4K Medium settings. In both cases we're performance-bound by other factors, be it single-threaded performance or GPU performance. This is a good precedent being set here by AMD, as even at such a low power, it's not enough to warrant noticeable drops in framerates, which is partly down to utilization with our AMD Radeon RX 6960 XT graphics card.

Touching on the Intel Core i9-13900K, although average frame rates and 5% lows at 1080p remained stable and similar, the 5% lows were much less desirable when testing at 4K. Average frame rates seem stable, but having much lower 95th percentile frames could become troublesome depending on the title, visual settings, and utilization of both CPU and GPU at lower power. Though, like many benchmarks relating to games, this phenomena is going to vary on a game-by-game basis.

Borderlands 3: 1080p and 4K Ultra Settings

Looking at performance in Borderlands 3, we can see that both the Core i9-13900K and Ryzen 9 7950X perform well even at just 35 W. This shows how powerful both these chips are for gaming, with high core counts which, despite operating at much lower power than stock, that it doesn't affect performance too much.

The only real notable result in Borderlands 3 was the Intel Core i9-13900K at 1080p, with lower 5% low framerates than the Ryzen 9 7950X. Although this could be an anomaly, we tested this three times, and all the results were similar. Even so, at just 35 W, the performance in gaming was typically unaffected, which shows that the game is more often waiting on our Radeon RX 6950XT video card.

Of course, gaming performance isn't going to be too much of a war of attrition to seek benefits even at lower power envelopes on the processor at resolutions such as 1440p and 4K, where performance is primarily GPU-limited. Even at 1080p, where there's a cross-over between CPU and GPU utilization, performance is still good.

There will certainly be a big difference at lower resolutions, such as 720p and lower. Still, users looking at a $500-600 processor, a $300-500 motherboard, and $150+ for memory are highly unlikely to be gaming at these resolutions, so we focused more on the realistic scenarios in gaming as opposed to purely synthetic ones.

Conclusion

So after lots of testing at various power levels on the Intel Core i9-13900K and the AMD Ryzen 9 7950X processors, we saw some very interesting results. While it's clearly established that both brands' current generation flagships are high-performance desktop goliaths in their own right, the performance of these processors doesn't scale down with power consumption in quite the same way. And that gives us some interesting results to dissect.

For our analysis, we've split our conclusion into two parts with a final summary; this allows us to make it more distinct in terms of benefits (if any), performance, and of course, if it's simply worth reducing the power on either the Core i9-13900K or Ryzen 9 7950X.

Core i9-13900K Power Scaling Summary

Starting with Intel's Core i9-13900K, we did experience some interesting results across the multitude of benchmarks and both games we tested. While the Core i9-13900K and Ryzen 9 7950X trade blows competitively when left at stock settings, Intel's offering didn't seem quite as performance competitive (and thus overall efficiency) at lower power envelopes. 

Despite being the more power-hungry processor overall, albeit, with better heat transfer than AMD's offering as evidenced by CPU core temperatures, the Core i9-13900K didn't scale quite as effectively as we would have expected. Or, at least, it didn't retain its high performance quite as well at lower TDPs when placed opposite AMD's best chip.

Using our CineBench R23 Multi-Thread test results as our baseline for compute performance, we can see how well the Core i9-13900K scales when tasked with rendering. Using the stock settings figure as our baseline at 100% performance, we can see that dropping down to 125 W; we saw performance sit at around 78%. As we dialed down the power to 105 W, which isn't a massive shift in power consumed, we got about 72% of the performance compared to stock.

Going down to the fan-favorite 65 W point, we saw performance levels drop to 56.6% of stock performance. Which, keeping in mind this is just 26% of the rated power consumption (and less still if the yCruncher power numbers fully translate here). So on a normalized basis, the energy efficiency of the i9-13900K has more than doubled (2.2x) when dialing it down to 65 Watts – it gives up a lot of performance, but it saves even more on power consumption. And if we do rope in those yCruncher measured power figures, then we're looking at something closer to 2.62x the power efficiency versus stock, primarily on account of the i9-13900K's incredibly high stock power consumption.

Overall, at the 65 W mark we saw a peak load power of 71.4 W, and a peak core temperature of 39°C. 

In our gaming tests, the Core i9-13900K performed equally well at all of the power settings we tested, which shows that despite curtailing the power limits massively, the performance for gamers is still there; not all games are created equally, and I'm sure there will be games that may see some drops in performance. The only pitfall we saw with the Core i9-13900K in our game testing was some slightly lower 5% lows in frame rate performance, which has the potential to be concerning, but it's going to depend on the game and the minimum framerates desired (e.g. does it drop below the 60fps mark).

Ryzen 9 7950X Power Scaling Summary

Things get very interesting moving onto the AMD Ryzen 9 7950X processor and the Zen 4 core based on TSMC's 5 nm node. At the top end of the power spectrum at stock settings, the Ryzen 9 7950X shows more efficiency in terms of performance per watt than the Core i9-13900K. Still, we observed some fascinating results as we restricted the power to the AM5 socket through AMD's Package Power Tracking (PPT) technology.

The first thing I want to point out is that, going by yCruncher, the Ryzen 9 7950X uses around 34% less power at stock settings than the Core i9-13900K to achieve similar performance levels. So AMD is already starting from a better place in terms of power efficiency.

Looking at our results in CineBench R23 Multi-Threaded, the Ryzen 9 7950X scaled exceptionally well from a PPT of 230 W down to 65 W. The most important results are obtained at 65 W, with CineBench R23 MT showing that the Ryzen 9 7950X kept 81.1% of its performance in that benchmark's rendering workload when compared directly to stock performance, all with a PPT setting just 28% of the stock limit. So to put things on a normalized basis once again, AMD's power efficiency has almost trebled (2.87x), keeping a lot of performance for a sizable drop in power consumption.

The catch here, however, is that the AMD platform as a whole was far more lax in sticking to its programmed PPT values, as evidenced by yCruncher power consumption. Despite setting the 7950X to 65 W, we still measured 90.3 W under that workload. So on the assumption that translates to CineBench, the 7950X's power efficiency gains aren't as impressive; we're looking at 42% of the power consumption for 81.1% of the performance, or a power efficiency of 1.93x over stock.

Looking at the rest of the metrics at 65 W, we saw a peak load power of 90.3 W, and a peak core temperature of 52°C. 

Finally, in the case of both processors, performance at 35 W wasn't precisely jaw-dropping, but it has to be noted that there are diminishing returns to any form of efficiency, and 35 W was, perhaps, a stretch too far for this much physical silicon. Despite this, the Ryzen 9 7590X held 49.3% of its performance in CineBench R23 MT, and the Core i9-13900K had just 30.6% of its performance at 35 W.

Reducing The 'TDP': Watts The Point

So when it comes to reducing TDP or restricting power to the CPU, some may ask, what's the point? Well, one example of where aiming for a higher-end processor and simply limiting power to it is in small form factor PCs. Smaller chassis typically have fewer cooling options available, and for the dinky systems, running a CPU at 253 W (13900K) or 230 W (7950X) can cause as many problems as it solves in such a tight space. Add any mid-range or high-level graphics card to the mix, and things will heat up quickly. 

It's worth noting that a typical 240 mm AIO premium CPU cooler, such as Cooler Master's MasterLiquid Pro 240, can accommodate between 210 to 230 W of thermal power generated, so anything smaller that's ample for SFF computing is going to be even less effective in shifting heat from the CPU to the exterior of the chassis. It's even recommended by many that users look for premium cooling, such as a 240 mm or, ideally, a 360 mm AIO CPU cooler when using one of these flagship processors.

Screenshot from Intel's Xtreme Tuning Utility (XTU)

It's not just SFF enthusiasts who can benefit from lowering overall power consumption. Still, those who are conscious of how much energy they are using aren't going to look favorably on 300 W of power being spat out from the CPU on its own, especially if there's no alternative to dropping a small percentile of performance for a fraction of efficiency. Less heat + less power = less problems.

Final Words: Zen 4 is Very Efficient, But Everyone Improves With Lower TDPs

Despite more affordable options capable of delivering solid gaming performance (check out our latest Best CPUs for Gaming guide for more details), in regards to taking x86 computing to new heights, both Intel and AMD can be proud of their achievements. Our testing and our independent reviews of the AMD Ryzen 9 7950X and Intel Core i9-13900K processors are clear that both are the cream of the crop regarding high-performance desktop computing. In fact, at the top end of the spectrum, both processors trade blows in compute elements such as rendering, encoding, simulation, and gaming.

The biggest winner in our testing is AMD with the Ryzen 9 7950X. The biggest takeaway from our analysis is that despite curtailing the max power consumption on the Ryzen 9 7950X by over 50%, plenty of performance remains on the table to be tapped into. Seeing the chip retain 80%+ of its stock performance even when the peak power consumption is just 42% is a very encouraging outcome. This makes SFF computing more appealing, even at the higher end.

Intel's i9-13900K, in comparison, doesn't fare quite as well. Though as it's clear both platforms are running well outside their "sweet spots" on the v/f curve for these flagship SKUs, it still benefits as well: a 65 W setting still gives us around 60% of the performance for 21%(!) the measured peak power consumption. The end result is that the i9-13900K sheds more power consumption on both an absolute and relative basis than AMD's chip, giving up more performance in the process.

Just keep in mind that TDPs (and PPTs) are better thought of as an "aspirational" value than a hard limit. That goes for both stock settings, and when power limiting these chips. In the end, neither platform quite adhered to our desired power limits, with AMD's being the worse of the two. Meaning that outside of stock settings, the 7950X ended up consuming more power at any given limit. But in keeping with our desire to focus on real-world performance here, this still offers a very valid take on what to expect from dialing either processor down to "65" Watts, as I doubt very many tweakers are targeting a specific wattage, versus just dialing down their power limits to save power and boost efficiency.

Ultimately, if you're short of space right now, you can still benefit from lower temperatures and reduced power consumption with either platform. Though when it comes to overall (i.e. best) performance, the edge goes to the Ryzen 9 7950X. With a nearly 2x increase in energy efficiency shifting down to a 65 Watt(ish) PPT setting, it's clear that the chip was pushed well past its sweet spot in order to achieve the best possible absolute performance. All of which means there's a lot of energy efficiency to gain from pulling it back to that spot. No wonder AMD decided now was the time to bring one of its chiplet-based desktop CPUs to the mobile arena with the new Ryzen Mobile 7045 HX-series processors – as audacious as a 16 core CPU is in a laptop, AMD's Zen 4 silicon is up to the task.