Find that thread on Biohaz site concerning a graphic.cfg tweak. I tried it and IT WORKS!!!! My fps increase in the A-10 Campaign 2nd mission at a point that i can now enjoy the game. I took the biggest value because i have 1gb of RAM. Read the post and try it. Before doing this, back up your graphiccsd.cfg file. Hope it will help.
Now here's the link for the thread: