I also have a 780ti, and was disappointed by the 900 series. So I've been waiting on the 1080, and expect to pull the trigger as soon as they will let me. I'll probably go with EVGA again. I got lucky last time using their step up program to go from a 780 to a 780ti, so maybe I'll get lucky again.
As for SLI, here is my take. Research the game you want to use SLI for. Make damn sure people/reviewers say SLI works and provides a benefit for it. If it does, THEN go SLI and be happy with just that. DO NOT expect all/most games to benefit or even work with SLI. A lot of times you have to disable SLI just to get a game to run. IMHO and experience, SLI is simply not worth the effort and hassle. YMMV.