Originally Posted by
FourOh
Maybe JPM can jump in here - my understanding is that PSUs are most efficient in the 50%-80% load range, so if you oversize your PSU not only do you spend money on the front end unnecessarily, you may not be getting the most bang for your utility dollar. Single 7970 systems are recommended to have a minimum of 500W, dual 850W (but 700W is enough if they are quality watts). I think you are wise to spend your money on the best quality PSU with the highest 80-Plus rating you can afford. I think either of the ones you posted are a good choice, though I'm partial to the EVGA lineup.
I used to buy cheap PSUs and I was always fighting with stability issues (my personal issues aside). I finally learned that forking over some extra money on a high end PSU saves a lot of pain, grief, and money in the long run. Good luck!