In most of my CPU reviews I tend to focus on light overclocking - the low hanging fruit if you will. Over the past few years the focus has shifted from absolute performance to performance per watt. An overclock stops being so interesting if you have to incur a huge power penalty to get there. That's the reason I've put more emphasis on stock voltage overclocks in the past few years.

The fact that I was able to get my Phenom II X6 1090T running at 3.8GHz with minimal effort was very impressive in my opinion. Remember that unlike Gulftown, AMD didn't get the benefit of a process shrink with the Phenom II X6. Six cores and nearly a billion transistors running at 3.8GHz with less than 10% more core voltage is awesome. But you all wanted more:

The most I could get out of the X6, reliably with air cooling, was 4GHz. It required more voltage than 3.8GHz but it's doable. The other important takeaway? It was fully stable in a 64-bit OS. In the past we've had issues with AMD's processors and ~4GHz overclocks in 64-bit Windows, but Thuban appears to have fixed that. I'm able to get into Windows at 4.1GHz but not what I would consider stable.

Note that at 4GHz the Phenom II X6 is faster than a Core i7 975 in our x264 encoding test.