Now is a bad time to buy any 600 card if you're updgrading from a 500 series card or older, wait for the 760 variant for more performance for your dollar. Coming from the 560 to the 660 wouldn't be much difference, 15/20 FPS difference at most The cpu bottleneck will be minimal.
Right now I'm waiting for nVidia to make optimizations for their fermi and kepler card with ARR because as of now the game is not full utilizing all of the gpu, even in non cpu bottlenecking areas.
