We were able to reach 4.26 GHz by raising the multiplier from x14 to x16. More clock speed should be possible by applying cryo cooling, but the 4.26 GHz speed we achieved is impressive considering we only used Intel's boxed cooler.

It was not very surprising to see the Extreme Edition 965 failing our overclocking tests at 4,533 MHz. Obviously, the limit of the double cores still is below 4.5 GHz when air cooled. However, we found it particularly impressive to see our test sample reach a 4.26 GHz core clock speed without any voltage increase. This proves that the C1 stepping offers noticeable improvement to the Cedar Mill cores (which are part of the Presler double core). When we overclocked the first double-core Extreme Edition 955, a noticeable voltage increase was required. This time, however, we could recommend running the Extreme Edition 965 at this clock speed if achieved without a voltage increase.

This shows an interesting aspect when compared to the Athlon 64 FX-60: AMD's processor usually requires a slightly higher voltage to achieve a 2.8 GHz speed, which in turn makes it impossible to take advantage of the Cool and Quiet capability, as it controls the core voltage by itself. The Intel Extreme Edition 965, however, can take advantage of its C1E mode when the processor is overclocked. Intel's processor thus offers the best of both worlds since it can be overclocked while the heat dissipation feature can remains active (when the CPU is in idle mode).

The design of Intel's reference cooler has not been changed.