What kills you is that your efficiency is terrible. You're getting 900kh/s out of your two cards using 700w, while a single 7970 can easily run 740kh/s using only 220w-250w. Much easier to mine with those kinds of numbers.
I just ordered a 7950. Do I need to voltage clock the card to turn it down to 220-250w?
Depends on the card, but usually, yes. Gigabyte and some others lock the cards at 1.25v stock which cannot be changed. This is very inefficient, especially when overclocked.
I'd only use either MSI TFIII or Sapphire Vapor-X 7950 cards as these can be software undervolted using Afterburner or TRIXX (under windows), or in some cases can flash with a modded undervolted BIOS which will reduce the power draw in Linux by between 20w - 40w under full load depending on your other clocks..