The 2500K is still a top tier gaming CPU. The GTX 680 has been replaced by the faster, cheaper GTX 770. I would just get a GTX 770.http://www.tomshardware.com/reviews/gaming-cpu-review-overclock,3106-5.html
I have a 2600K and a GTX 460 1GB. It was a great card but the new games of the past year are really too much for it. I plan on getting probably a GTX 780 next month. I have no plans to upgrade my CPU though.