I'm not having any framerate issues at all.
I have 4xMSAA enabled (only possible with DX10), I set anisotropy filtering up to 16x (default is 4x), I enabled vsync, all graphics options are on, and my framerate is 100% of the time at 60FPS. I haven't disabled vsync to see what kind of framerates it goes up to, but I don't really care for that. As long as it can maintain a solid 60fps, I'm happy.
My single GTX 275 and Q9550 definately has some massive frame drops at random moments with 4xMSAA and max in-game settings. It runs at a locked 60fps most of the time, dips to the 50s and high 40s here and there, and then suddenly for no apparent reason some corner of some random room will cause a drop to 30fps. It's rather weird and I wonder if it is a DX10 issue, but forcing DX9 gives me a ton of artifacts for some reason, so I'm staying away from that.
It also should be noted that the game is very sensitive to framerate fluctuation, reminds me of Far Cry 2. Dropping from 60 to 45 feels like dropping to the 20s for some reason.