Here is a link that will show you in game performance of the 770 in SLI vs the 780 ti. i know it’s not the 770 superclocked or 780 ti classified, but you will get a general idea. It is better to have a single powerful card vs two cards in SLI, you start getting diminishing returns when adding more GPU’s, adding a second card doesn’t mean you are going to get twice the power. Don’t quote me but I think it’s something like %50 for a second card and it continues to drop ass you add a third and fourth. There are still micro shuttering problems when running multiple GPU’s, granted they are getting a lot better but there are still problems. By the time you need a second 780 ti I am sure that the SLI/Xfire issues will be corrected (I at least hope they have it fixed by then).
I say go for the 780 ti Classifiedhttp://www.anandtech.com/bench/product/1064?vs=1072