Ok a few quick tests just to show variation with the shader setting, DX10 path-
All very high
How I play, all high, shaders, textures and water, very high
All Very high, shaders set to high-
Legend's suggestion, texture, object, water, sound = VH, all else high
Medium shaders, rest to very high
All medium for the hell of doing so-
If you are having FPS problems definitely set it all to high and perhaps even reduce shaders to medium in extreme low performance instances. BTW I tried Texture, Object, Water, Sound, Very high, and all else high @ 1024x. I got 54FPS in shot one and 43 in two.