Wait until the end of February. The GTX 590 and Radeon 6990 are about to get launched. That means that the high end cards prices will be forced down a little. It might be only $20 and $50 on deals--but I think your 4890 can hold out until then.
I'd go with the 6970 because it has a larger frame buffer. And when you crossfire/SLI a second one down the line and run 3 monitors, you'll want larger than a 1280MB frame buffer.
I'm not going to crossfire/sli or run 3 monitors. For a single 1920x1200 monitor would you still recommend the HD 6970? Also, is my Q6600 going to hold the 6970 or GTX 570 back? If so, would I be better off going with the 6950? Thanks!