I'm on a Q6600 @ 2.8GHz with a 5850 1GB, 4GB ram. Metro was fine, but Caspian brings my pc to its knees. I use 1680x1050 Res. I have tried Low, Med, High and Ultra settings and the difference between High and Low, in FPS terms is negligible if any.
FPS ranges from 20 to 40 typically, which "feels" pretty low in this game. It's not really very playable when compared with the perfromance I get in BC2. FPS in the areas where you want it to be high, around the centre of the map, drop quite considerably, especially during firefights.
I may as well play at high because the difference in FPS between that and low is almost nothing. As such, I have come to the rather disappointing realisation that the Q6600 just cant hack BF3. Those kind of results suggest that the CPU cant keep up.
Not really complaining though as Ive been meaning to upgrade anyway, just not quite so soon.........