If you do go for another 780, id strongly advise going with a reference design. If you bung two non refs together youll run into heat issues on the top card. That aside 780 sli is still pretty powerful. Though with newer games it remains to be seen if 3gb of vram will be enough.
Yeah just saw that 10 minutes ago or so, Someone had a Windforce and Classified 780 and one of them was in the 90's!