I don't agree with 7950 recommendation. After my 2 dead 7950 GPUs I went back to Nvidia taking MSI 660Ti PE OC Edition - and this was the best choice I've ever made.
I was quite lucky because I got myself 85% asics card which after OC resulted in:
Core with kepler boost: 1333 MHz
Memory effective: 7400 MHz
3583 GFlops
31992 MPix/s
149296 MTex/s
111972 MVts/s
177.8 GB/s (!!! - almost as good as gtx 670 although it has wider mem bandwidth)
So these performance values in GTX 680 STOCK looks like that:
3090 GFlops
32192 MPix/s
128768 MTex/s
96576 MVts/s
192.3 GB/s
Basically I gave myself GTX 680 performance (need some more memory tweaking) but saved up loads of $.
You just have to learn to OC the kepler because it's much harder than OCing different cards. But after You do, with a little bit of luck, You can get great performance.
This is my 3dm 11 score with mem to 7000:
http://www.3dmark.com/3dm11/6222061
The only flaw of 3dmark11 is that it doesn't cooperate too good with kepler drivers and it results in power percentage draw goin over 100% and card is sometimes throttling in 13mhz increments which results in a bit lower score (it should be around 10500 on gpu score).
Still - I don't throttle in any game, even with resource hog far cry 3. And with 1080p, everything to ultra, and aax4 I get stable 45 FPS plus no latency so I don't get any stutter.
This card can be amazing but You have to treat it well.