Leave things standard for draw, pushign anythign over that isn't going to do much visuall but draw and reasjust the size of the BG, texels and textures to fit your screen.

I'm assuming for the 6900 series, so it shoudl play everythig nhigh and very high for teturing draw, prob AA at 16x, MSAA and Anisotropic 8-16x (8x is optimal for this game).

Ambient and the field of view is where it strains GPU's, personally Field of view jsut ruins it for me. Ambient lighting can strain the system but add better detail to dark areas. Set it at standard or performance. if you use it and you should be fine.