If I was you I would wait for the new HD7xxx series and whatever Nvidia is going to release, now isn't the best time to buy with the new tech coming around the corner and your current card isn't exactly terrible or outdated.
And that waiting won't cost $400 for sure :p
Nvidia's Kepler's were originally slated to be released (well... after nvidia delayed it... and technically never gave an actual "release date", just a time frame) in March/April, but with limited exposure with budget cards first (GK104 chip); the flagship, high end cards (GK100 chip) was originally planned to follow suit sometime in Q2, probably in early or mid summer.
But now reports are coming out that nvidia has pushed the time table on Kepler to be released in weeks (probably due to the AMD's new cards), not months so who knows what nvidia will release next month. It could very well be the full line of the kepler series, which could lead into a stiff pricing war across the whole line of price points.
This would surely help reduce the prices of older gen cards and AMD is known to be quite quick with changing prices, as apposed to nvidia (and Intel for that matter). AMD has to stay very competitive to keep their little bit of market share in both cpu and gpu's. Lots of rumors on Chinese forums and lots of paper benchmarking has risen (although pretty pointless without real benchmarks). Some of the GK104 specs sound better than the 580's and those are suppose to be priced between the current 560 and 570's.
I'm not sure how quick their 680's would be released since their product development time is much longer for the GK100 as it'll be used in the Geforce, Quadro and Tesla lines. If I was a betting man (and I'm not), I'd say the GK104's would come out next month and the GK100's a month later at the earliest. Even if they had gotten the samples in early December and got all the bugs fixed in a month, they still have to mass produce the chips, get their quality control up for their runs, supply the board manufacturers, who then in turn have to design (well nvidia does the reference boards) and build the cards while marketing has to do all of the necessary collateral, packaging and ads to market the card. And that's quite a feat to do in a few months if everything went to plan.
Its all speculation right now since very little info actually comes out from nvidia's mouth.