I have my FPS locked at 35. I get the same result regardless antialiasing and other goodies turned on or OFF. In my case (and that goes for the most of us here), the limit is set by the computer and it's memories.
I think that's an issue with ATI. I couldn't get video card settings to effect image quality or performance (when turning settings down).
My friend has a older Nvidia card and moving video card settings on that thing makes a HUGE difference in both areas.