in many synthetics gaming benchmarks like firestrike, heaven, valley etc., a single 780ti with a healthy overclock... 1.3ghz or so, will very nearly match sli770s. in real world gaming, where sli scaling isn't nearly has high as it is in the synthetics, and especially in non optimized games where sli scaling is many times around 70%, the 780ti will perform on par or better. if you dont already own a single 770, there is no point whatsoever in buying two 770s. just get a single high performance card. if your building a new system around sli, you have to account for the added motherboard cost for a sli/cfx support for full speed across pcie lanes, and you need to account for a 200-300 watt higher rated power supply. once you have added those up, you might as well just go sli with a top tier card. unless you already own a previous gen/current gen flagship model, it is not cost effective or smart to jump to sli/cfx with a non flagship model. that said, both amd/nvidia flagship cards offer plenty of gpu horsepower for any current game on single monitors 1600p or below.