I used to run The Sims 3 on Windows Vista 64-bit at 50-60 fps.. But after changing to Windows 7 it dropped to 30-40. That's the only game I had issues with. I played CODMW2, Arkham Assylum and dirt 2 at 50 fps average. Would you say is a driver issue? I think that's a possibility since I used to have a terrible fps downfall on the dirt2 menu but after updating the drivers that problem vanished. Did anybody had a similar problem with that game or another?
If you use the default drivers out of Windows 7 then yes, that's what will happen. Updating to the latest drivers for your chipset will definitely help in just about all cases. However, I do know that the latest ATI drivers killed FPS for me, so I had to roll back to the previous version.
I'm using the Catalyst 9.11 drivers currently. I tried the 9.12 and it decreased my frame rates, so I rolled back to the 9.11 drivers. They just released the 10.1 drivers and already, some people are having issues, so I'll probably hold off on those as well.