The 770 is an absolutely fantastic card considering the price point, but it's really just an upgraded 680, which means it's very well-matched to your 2600K. In terms of bang-for-the-buck, upgrading your current system to a 770 would probably be the best thing you could do.
If you wait and build a new system in the next 6 months or so, in order to get the same gaming performance as you would by upgrading to a 770, you're looking at on the order of about $1100ish minimum (4670K, AsRock mATX build, GTX 770, low-end PSU, no SSD) unless you can scavenge parts from your old system. So you'd have to spend about 2.5 times as much for the same performance gain, and you'd lose the i7 advantages in well-threaded applications (if you care).
In order to get *better* performance from a new system than you would by upgrading to a 770, you'd have to upgrade to (a) a 780 (add $200-250), (b) SLI 760s (add $150ish plus $50ish for supporting hardware), or (c) an SSD (add $175-200). So you're looking at spending $1300ish for something that's marginally better than what you can get now by spending $400-450.
I wouldn't do it. If you really have the itch to build a bleeding-edge PC, save up just a little while longer and buy a 780 (also an amazing card) and then build a new system around it later. But if you want the most value while still maxing out games, grab the 770 and then wait a generation or two.