Important Gaming build Q's

[kitkatcam]

So... I am decently experienced with computers but I want to see what you guys think about this. 

I have a i7 4790k which i now see is a bit over kill for my GPU which is a GTX 780 EVGA ACX 3GB model

so i was wondering if I were to upgrade my gpu power if i would be better of with a GTX 980 or a GTX 780 SLI. 

the Sli would cost me much less than the 980 since i already have half of it, so what do you guys think.

[The_Stig]

What resolution are you playing at?

[kitkatcam]

I am planning to be running at 1080p across 3 monitors. with a possible 4th one as an auxiliary. 3+1=4