At that resolution, your gtx 460 will be enough for a year. You should be able to max everything out without any problems. a 570 at that resolution would be a complete waste of money. Hell, the next upgrade to the 570 (a 670 i guess) would still be complete overkill.
Unless you are planning on upgrading your monitor to 1080p, I wouldn't worry about it. When the next generation of cards come out about 8 months or so, upgrade then, because games will probably be much more demanding on a gtx460. Even then, you don't need to get the 670 (upgrade to the 570). Heck, if you are finding that the card you have now is not sufficient enough for you, get a GTX 560 or a 560ti if you want to spend another $40 on it.
Okay, I think that's what I'll do. I'm getting the recert sparkle 460 768mb. It has a lifetime warranty that's the only reason I'm going recertified. For $100.