Don't get SLI. First of all there is a micro-stutter issue. Secondly, a GTX670/680 can play most games at the highest quality anyway.
Since you're considering SLI, money's no issue. Maybe get this 3-slot card (the one I have):
Asus GTX680 DirectCU II
(the TOP version with 1139MHz, not the slower one.)
if it was up to me to get a 680, id get the msi lightning 680. 2 slot and its cooler than the asus 3 slot (or so i heard)