well I just finished mass effect 2 with a steady 60 fps ad 2048x1152...
so not really..the only game that seems to have fps issues is crysis for some reason..they fluctuate a lot from 60 fps to 15 in a matter of seconds..
Crysis 2 is unknown as although they state the pc version will be for the pc it is also a cross platform version so who knows.
Obviously with AVP it might use some dx11 stuff but I am not sure how much and if it will be noticable. Really you have nothing to lose by waiting until the time that you cannot get the performance you want.
The tessellation on AvP will probably need a 5850 minimum to use it fully.
A 5970 will be an upgrade, but at that resolution you probably won't notice 60FPS to 80FPS.
5970 really shines at 2560 x 1600 with AA and 3 * 1920x1080.