My average FPS is always over 50, but the minimums seem to drop a bit low, around 33 (sometimes much lower). Makes reactive gameplay a little more difficult when the game randomly slows down. My specs (custom built):

HD 6950 1gb
i5 2500k @ 4.2Ghz
8gb (2x4gb) DDR3-1600 CL9
7200 RPM HDD (only 56.6% capacity filled)

Computer is otherwise well maintained, tested Prime95 stable for 12+ hours.

I normally play near maximum settings, so I have a lot of room to work with. Is it the 1gb of GPU memory, and if so what settings are the biggest memory hogs?