yep, it depends on the game... for example, if you play Warhead then NO you wont be able to max the game out but lets say you play BC2 or Dirt2 then YES you will have more than enough frames regardless of the settings.
I use a single 5850 @ 1680x 1050 and the only game I cannot max out is Crysis (Warhead) and metro 2033, all my other games get over 80 frames at MAX detail settings.
I highly doubt that you can max out BC2@1680x1050 and still get over 80 FPS on a single 5850?
I have a single 5870 and hardly get over 65 FPS, but that's with HBAO on, bloom on, everything on high, 16xAF/4xAA. With 8xAA I cannot even Vsynch@60Hz...