Hate to say it, but if price isn't an issue...go the GTXs. Drivers are better and SLI scaling is better. The 480s are beating the 5970 even with the rather adolescent drivers nvidia has...so you could expect even more performance. Plus, cheaper last time i checked
But if you do decide to go ATI, I got 5970s in quadfire, and that is pretty damn powerful...but overkill. They run quite cool so overclocking to buggery is quite easy just on air. And most bugs are gone with recent drivers (more coming out within a few hours of this post also).
Everything ATI brought to the table 8 months ago, Nvidia has equaled or outdone, which isn't really a big feat. They had a 6 month buffer and only came up with the 480? Pretty weak if you ask me. Eyefinity/Surround, DX11, 3D etc. Your power bill may be a large chunk bigger...but 480s are the better cards IMO.
If you do a little bit of research, it isn't hard to see this.