I think we may need to briefly consider the effect on more RAM on this game.
I have a friend who's in my clan who runs a setup very similar to mine... he has a Phenom II x4 @ 3.4ghz with a single 5770 (performs equal to 4850/4870) ... but he has 8gb RAM.
He SAYS he's running @ 1680x1050, with everything on high, with 8xAA and 8xAF. Vsync is off, HBAO is on... and he's reporting 80-90fps.
Wait, what? I get 38-55 fps @ 1280x720 and 1280x1024 with everything on high, 2xAA, 4xAF, vsync off, HBAO on!!
Why the big disparity?
It's not the video card, is it Does the soft shadows DX11 path for the 5770 speed things up? I don't think so, at this point I think it's that his rig has 4gb more RAM.
It'd be nice if someone here could test this game with 4gb RAM vs 8. Anyone up for it?