I would always purchase the best SINGLE card I could afford. I don't want to deal with sli/xfire driver issues, additional heat and wiring, etc. Unless you are going to be a hard core, multi-monitor, hi resolution, eyefinity etc etc user, a SINGLE card, IMO, is always the way to go.
Depends on your needs along with the games and resolution you play at.
“NVIDIA says if you're looking to upgrade from a GTX 560 Ti or similar $200-ish dollar card, this is the GPU you want. After looking at the benchmark scores, it's hard to argue with that logic.As far as bang per buck goes of course 2x gtx 760 out performs a single gtx 770.However keep in mind power consumption and scaling become a factor with sli/xfire setups supposedly though i personally have none of these issues with my 2 x gtx 670 in sli at least not that i notice so i cannot comment to much there.There is one other thing that is worth mentioning and might be important many games support SLI but some do not.