FPS difference between a 3840X2160 monitor vs 2560X1600 monitor(on ultra setings)?

[m1234]

I am building a new rig and want to play on ultra resolutions (3840X2160) with really good fps.with 2 way sli gtx 780 ti superclocked.
please tell me a good answer.

 

[cuecuemore]

Framerates with parity quality going from 25x16 to 4k will be about halved. I'm not sure what you mean by "worth" it, you need at least 2 high end cards to think about 4k, so you're not wasting any of the GPUs, if that's what you're asking.