Windows 8 vs Windows 7: CPU performance
 

Two things are clear. AMD's claim that its processors should run better with Windows 8 seems to be unsubstantiated, at least the benchmarks do not confirm this. Secondly, just like the gaming performance, there is no noteworthy difference between CPU performance in Windows 8 compared to Windows 7.

http://uk.hardware.info/reviews/3549...pu-performance