Both are a waste at 1080p, a single 760 would do you fine.
Between the two options though, a 780 is a better pick. Its a little slower and more expensive, but SLI solutions with two midrange cards are better kept for when you don't have the funds to go for a higher tier card, so instead invest in e.g. a 760 now and buy the next one for SLI in 6 months time. You'll have less heat, less noise, less power consumption, no SLI troubles (though few and far between anyway) and you'll have an easier time selling them on.