I wonder if this will help with Mirror's Edge? I get 60 fps on every other game (outside of Crysis), but Mirror's Edge with PhysX enabled results in drops here and there (nothing serious, but I would like a perfect framerate). With PhysX disabled it's a solid 60, but I love those physics. Anyone tried it out to see if there was much of a difference?
How big are the drops? If the drops are drastic, then you might need to uninstall PhysX and reinstall it again. On the old setup, I had problems with PHYSX scenes dropping down to less than 20FPS. They were gone once I reinstalled Physx.
If that doesn't solve the slowdown, then you probably need another GPU as a dedicated PhysX processor. Having a dedicated PhysX processor improves performance quite a bit. That's why, even with 4 GPUS, I got another GPU just for PhysX. With the current setup, the framerate never drops below 60 in Mirror's Edge with maximum settings in 1920x1200, 16x AA, 16x AF.
Left 4 Dead still drops into the 20s during swarms 
but the less-populated areas jumped by about 10fps
I'm pretty sure it's a Vista drivers problem. I noticed some drops to like 40 FPS on my current setup so I knew it couldn't be a hardware issue.
I switched to XP and all the framedrops were completely eliminated.
COD4 and COD:WAW also perform better in XP. Even in Vista, they run at well over 60fps so I don't bother switching over to XP for them. However, if you're only getting about 30-40 fps in COD:WAW, it's worth checking it out on XP to see if you'll get an extra 10-15 fps. More importantly, there'll be less slowdown. On my old setup, COD4 will have pretty big framedrops whenever there is a lot of smoke but that only happened in Vista.
