bit-tech published a look at Windows Vista SP1 gaming performance

On the whole then, the benefits of Windows Vista Service Pack 1 from a gamers' perspective are quite small at the moment -- you should see similar performance to what you're getting with an up-to-date vanilla Vista installation with all of the latest hotfixes applied. That's a good thing in many respects, but it won't fulfil the hopes of the Service Pack magically increasing gaming performance for gamers. It does add quite a few new features though and if you're stuck deciding between installing it and not, we recommend going through the change log to see if any of the changes are useful to you. Of course, there is another side to the Windows Vista Service Pack 1 coin---2D application performance---and that's something we're going to be investigating later this week.

Windows Vista SP1 gaming performance