I have a 3.2 single, with 3 gigs of ram and a x850 video card. I get a small hit, 5 fps, a bit more in furballs with the hi rez pack.
I stick with the 512 texture tho, and bumped my antialisen up to 4X and it runs better FPS, and looks about the same. About the only time you really notice the extra eye candy is when your looking out your plane and you see your wing.