Just remember the Asus 680 DC2 is 3 slots. Its a mammoth of a card. I think on a Z77 board they'll be sandwiched together, although they'll still cool well and look really slick in a case.
On my board, two slot cards in CFX/SLI allow one slot of breathing room between the cards, with three slot cards there would be no room. From looking at images on your board, it'll be sandwiched. It should be fine with such good coolers though.
80 plus certified is a rating of efficiency, not really constant output which you should be looking at. OP, look at your PSU sticker and say how many amps are on the 12V rail. It might just be easier to tell us the brand of it too. If its Corsair, XFX, Seasonic, Rosewill and a few others you'll be fine.