ATI and Nvidia have had plenty of time to fine-tune their graphics monsters for Windows 7, so with the latest drivers, Extremetech answers that burning question: Is Windows 7 or Vista faster for games?
Their test rig used a Core i7 with 3GB of triple-channel memory running Vista vs. Windows 7 beta build 7000 (the one you're probably running). The cards tested were Nvidia's GeForce GTX 285 and GeForce 9800 GTX+ and ATI's Radeon HD 4870 X2 and Radeon HD 4850. And they checked out a whole bunch of games, from Crysis to Left 4 Dead.
Medium-length answer short: It's pretty much the same! Sometimes Vista wins, sometimes Windows 7 will squeak out an extra frame per second over Vista. Overall, across all of the games tested, higher end two-in-one cards seem to eke out most of their wins in Windows 7 though, especially with the ATI cards.
It bodes pretty well. You definitely won't lose any performance moving to Windows 7, and it's likely going to get even better as we move to the final OS and Nvidia and ATI keep cranking out drivers. So maybe not today, but one day, Windows 7 it seems like will run Crysis (and most any other game) faster than Vista. Check out all the benchmarks for every game over there: [Extremetech]