My 7790 results...

296 mhash (guiminer -v -w 128 -f 1 1200/200)
246 khash (cgminer, tc 8000, w 128, i 17, 830/1500)

I have three and they hardly use any power. I'm running them stacked in a case and the fans are so quiet I can't hear them.

That said, I am looking to build a rig with 2x7950 or some other beastly cards because I want more hash.