As mentioned the problem here is the graphics drivers that are not optimized for Vista. ATI has released their catalyst drivers which improves the performance, while Nvidia has yet to release anything better optimized. In fact, Nvidia has yet to release a driver to run cards in SLI in Vista, unless you are running their newest 8800's.
The primary reason for Vista's Aero desktop running in 3d is so that the OS doesn't need to switch between a 2d and 3d mode. You would notice a smoother transition if you were to Alt-Tab between a 3d game and the desktop.
I'm pretty sure with better optimized drivers for Vista, that you'll see as good or better performance with games than in XP. Unfortunately you'll need to wait for Nvidia to get around to that.
Bookmarks