MalakiArtook :
Francisco Costa :
Fot those resolutions you don't need GTX 780 SLI... GTX 780 Ti or R9 290X will be enough. Or even a well overclocked GTX 780.
Yeah It's not recommend to build a computer with 2 lessor card. you should almost always go with 1 of the best card for your budget for gaming. SLI is more of something you do years down the road to squeeze relevancy out of your rig.
The two lesser card thing applies to lower end GPUs: 750 Ti (I believe), 760, and 770.
The performance difference between the 780 and 780 Ti isn't that large, and two SLI 780s would easily trump a single 780 Ti. Whereas if you were comparing two 760s or two 770s, their performance is closer to a single card: 780/ti
To the op, go with the SLI 780s, you won't need...