CPU Scaling: Intel
One of the rumors I recently heard suggested that Blizzard made some threading optimizations to the latest build of its engine. Now, I never benchmarked scaling performance pre-patch 4.0.1, so I'm not sure how much CPU muscle the game exploited previously. However, disabling one core at a time reveals that two cores is all you need to realize the GeForce GTX 480's maximum potential.
Not content to simply generalize about processor performance using an overclocked Extreme Edition CPU, we built up a P55-based platform as well and dropped three more chips into it, using various over and underclocked settings to isolate the effects of clock rate.
Starting from the bottom and working up, Hyper-Threading does little (positive) for performance, as that's the only thing differentiating the Core i5-655K from the Core i3-530 at 2.93 GHz.
Pushing the unlocked chip's clock rate up to 3.2 GHz does add a few frames per second, though. And boosting it up to 3.73 GHz contributes even more.
However, the fact that Intel's dual-core Core i5 at 3.73 GHz can't match the Core i7-980X with two cores enabled at 3.73 GHz makes it clear that there's more to performance in Cataclysm than frequency. The quad-core Core i7-875K nearly hits the $1000 chip's mark using four cores and 8 MB of shared L3 cache, so perhaps this is a matter of cores and cache. After all, the Core i7-875K at 2.93 GHz also beats the Core i5-655K at 3.73 GHz.