Since you're gaming at 1080p it may be worth it for you to just spend the extra money on a GTX 470. If you can live with occasionally lower AA and AF settings then just get a GTX 460 and add another one down the road. By the time two 460s in SLI aren't enough for you you'll probably be upgrading again anyway. A 460 now and a second one latter is the most reasonable choice.
Of course this comes from a guy who bought a 5870 when they were still $400 to game a 1680x1050 and is thinking of getting a second one
. Sometimes it's just about want.