Little late to the party but id never recommend 2 generation old vid cards to anyone, it leaves no upgrade path. A single 7970 wouldve been the same price, plus or minus a few bucks, and left you a ton of options for upgrades in the future. Just my opinion tho, not meant to get anyone riled up but it probably will anyhow.
i agree. in raw power 480 sli may be better(cant say it is because dont have either card)but you used up 2 pci slots already and dont have much headroom for upgrade. always get the single best gpu that you can afford, and maybe get another like a year down the line. that being said, and since you have already purchased them, those will be fine for 2 or 3 years as long as you only play at 1920x1080 or lower