Gaming Performance Compared: Windows 7 vs Vista vs Windows XP
 

While there were a couple of cases where WinXP outran Windows 7 and Vista, for the most part Windows 7 wins more than it loses, especially when you factor in multi-GPU technologies like SLI and CrossFire. In fact, if you’re a Windows XP gamer with SLI or CrossFire, I’d definitely urge you to upgrade to Windows 7 as soon as possible.

Windows XP’s origins date back to Windows 2000, an OS that was never designed for multi-GPU.

On the other hand NVIDIA and ATI worked closely with Microsoft to get Vista’s DX9.0L and DX10 APIs to scale more efficiently with SLI and CrossFire. Memory management tweaks found only in Windows 7 increases this even further, allowing SLI and CrossFire to scale even better under Windows 7 in comparison to Vista in many games.

http://www.firingsquad.com/hardware/...ng/default.asp