Nvidia 560 TI are good but considering you already have a 460 which is quite good you should be able to pick another one up cheap as chips. The performace is amazing. Just make shure you know how to SLI otherwise you can run into ALOT of problems.
Yeah I am going to have to say get another 460 as well, if Nvidia does announce the new cards in early 2012 then you will be able to upgrade with less regret then if you spent $350 on a 570 now.