Get a GTX 768 mb ram, my frames in that game, in multiplayer with about 9 other people, never go below 35, usually much higher. ok, maybe when a nuke goes off, but thats it. ps-I am running at 1920 widescreen.
one more thing, are you running vista? that may be the problem, as I am in xp.
And you may want to lower some effects rather than resolution.