get the XFX HD5970 Black Edition. I bought one a couple of days ago and runs everything maxed incl warhead at 58FPS. It devours everything. A truly remarkable card. The good thing about the Black edition is it comes with XFX's own guaranteed overclocking tool so when you need a bit more ooomph it's there on tap. It also runs alot cooler than 480.
^psycho, the XFX 5970 Black Edition has higher clock speeds than the regular 5970 and is more like two 5870s in CF, so the difference is a bit more than 1.4 fps. Considering you have quad 470s you can't really be talking about bang for the buck .
Anyway a 5970 is generally faster than a single GTX 480 so if you can afford it, and your case and PSU can handle it, then go for it. If a 5970 is pushing your budget, then you may want to get a GTX 480 now and then add another one latter to run in SLI when you feel you need the extra power.
If you're concerned about the best bang for your buck then you may want to consider two GTX 460s in SLI instead.
Hey, guys... you seem to be missing the point. The OP said both a) He wants a single card solution and b) it's not exclusively for gaming.
Under those circumstances I would recommend the 5970 2gb edition (is that the Black edition?).
If a 2 card option were on the table, then CF 5870s is going to be cheaper and killer, SLI 480s is going to crush but be expensive. CF 5850s perform very close to a 5970 for about $150 less. GTX460s perform surprising close to 5850s so you could save a bit more there.
All depends on budget, and given that the OP is looking at a $750 card, IMO the best way to spend that money would be SLI GTX470s as it's around $700 and will perform about as well as CF5870s, both situations perform better than a 5970 or a single 480.