Hi Garfo,
I only have a single EVGA 780 superclocked/ 3770k @ 4.5 at the moment. Waiting to see what happens with the 390x or I may go titan x.
Some average benchmarks with single 780 sc (max settings)
I like my racing so start with
project cars - vsync locked fps @ 30fps (far from ideal)
assetto corsa - 50-60fps
battlefield 4 - 35fps
sr4 - 55fps
something old COD MW2 - 60fps
dying light - 30-40fps
crysis 3 - 30fps
bioshock infinite - 35-55fps
tomb raider - 45-60fps
So not optimal but it does alright considering I bump everything up and run at native.
IF you have similar gfx horsepower you can bring it down to 1440p which makes a world of difference I can then max out most of the above.
The display is actually very nice for a TN panel. The colour saturation is better than any TN I've used in the past. Brightness level is good obviously viewing angle is a little limited still but not a problem for me sitting in front of the screen.
The vertical viewing angle is more limited than left-right but the excellent stand allows you to get the best possible eye level to suit.
4k is nice but dont expect retina sitting relatively close. That said I wouldn't personally want less res on a 28" screen having now tried all flavours. If you like gaming its a nice screen very fast panel and although I still like a little AA you can for the most part play at 4k without AA and it looks pretty clean.
I would love to go triple with these monitors but the bezel is fairly thick. There is a popular channel on youtube where the guy has just bought a triple setup and 2 x titan x!
https://www.youtube.com/watch?v=wa5H4fDJUWE