I have never had any sleep problems on my Sapphire OC 7970 or Sapphire OC 7850.
The HD7970 is about as fast as a GTX 680 and faster than a GTX 670 when all are max oc'd.
http://www.hardocp.com/article/2012/05/14/geforce_680_670_vs_radeon_7970_7950_gaming_perf/3
Load power draw is not great, especially when overvolted, but you will likely spend more time at idle (web surfing, Word, posting at AT Forums, checking email, etc.) than at load.
The only real weak points of the 7970 are pricing and lesser feature set (no adaptive Vsync, CUDA/PHYSX, worse multi-GPU support, no GPU Boost). But you can sell the mDP to DVI adapter that comes with the 7970 and the 3 free games as well, and that drops the price of a 7970 close to that of a GTX 670. And the 7970 is ~10% faster than 670 when both are max oc'd.
AMD currently is way better at multi monitor support with 3GB VRAM and with presets and hotkeys whereas NV is stuck in the stone ages where you have to go back to their driver menus all the time to switch. On the other hand they don't need DP to DVI adapters, either.
Note that 7970 also has non-gaming advantages (HPC) but most people don't need it.
In short, I think the three cards are priced fairly right now:
Slowest 670 nevertheless has best bang for the buck of the three.
7970 is a little faster and a little more expensive even after selling the cable and games. Also has more VRAM though that isn't likely to matter for quite a while.
680 is merely tied with the 7970 when both are max oc'd but is also more efficient and has a better feature set overall, at least for single-monitor gamers. Won't likely miss the extra VRAM unless you're going multi-monitor or keeping the card for many years.