i would really hold out for a 680 especially if you're going to spend $300 on a 570 anways. 680 for $500 doesnt stay stocked for very long however. the HD 7970 (if you don't care about amd versus nvidia) sells for $480 and it just a little bit slower, but you wouldn't even notice the difference if you're going to use just 1 monitor on 1980x1020. just make sure your power supply is good enough for whatever you want.
The hardest thing to do is wait and not know when something is going to be in stock and then you buy something because you can't wait any longer and the thing pops up in stock. If you want to pay an outrageous price there are 680's to be had.
A GTX 570 is an upgrade to the 460 and would be a worthwhile upgrade but if compared to a 680 then it's not a fair comparison , the 680 is a much more powerful card and the price difference shows it. The GTX 570 is three levels aboven the GTX 460 so that makes it a good upgrade.