Didn't AMD release the HD7850 recently? Might be worth checking out if you're a gamer. The drivers might cause problems though since it's so new.
As for the other stuff:
-4GB RAM is more than enough
-any quadcore x86 CPU should work
-a fast HDD/SSD can remove the stuttering when stuff loads.
Settings are usually:
-2x or 4xMSAA
-8 General Drawing (9 and 10 are supersampling)
-5 Background Drawing (just increases the background resolution, can be maxed for fast GPUs)
-Shadows to lowest and disable ingame (they look horrible anyway)
-Textures and filtering to max
-Ambient occlusion off (is broken and driver profiles seem to disable it anyway)
-Depth of Field really just depends if the user likes blurry stuff, the hit on performance is about 5-10%
I would always try to run the game in the screen's native resolution as this prevents qualitiy loss that comes with resizing to fit the pixels.