It's not better for sure
First of all, it overclocks good, but so does GTX 680.
Secondly, it might scale a bit better with triple monitors, but it's a pain to set it up: you need display port adapters with HD 7970, and with GTX 680 you just plug it and it works.
Thirdly, by going with nvidia, you get many nice features: TXAA, FXAA, PhysX and Adaptive VSync. Their 3D vision is much better than AMD version as well.
You can read this review:http://www.tomshardware.com/reviews/geforce-gtx-680-review-benchmark,3161.html