Budget is flexible as it would be cheaper than a new rig.
DX11 would be fine if/when I upgrade to Win 7. I'll let that be out for a bit before I upgrade.
I play at differing resolutions. Playing at the higher res even on SLI beat my current rig up on Crysis. (I thought SLI would be definitive difference once I went SLI, but I didn't notice a huge difference.)