It's not just you or SLi, it's the game. I run crossfire and have similar results. If it wasn;t for the crossfire bug having my second GPU show 99% both would be at 70ish. Also, the game should be running much smoother but it barely looks any better than me running 1 card.

I am on 7970s mind you with them OC'ed to 1080/1450.