Atm i have GTX560Ti so i only run 1920x1080, DX9, high for maximum fps, but probably upgrade to GTX580 or HD7970(when it comes out), so hopefully i can play 1920x1080, DX11, ultra, high texture and still get ~100fps.
I think ultimate C2 setup would be 3x 27" Samsung S27A950D 120Hz(5760x1080, DX11, ultra, high texture, max aa?) with GPU(s) fast enough to get 120fps minimum fps.