JackNaylorPE :
No pair of GFX cards can satisfactorily (60 fps) drive 4k. 4k is also limited to 60 Hz (75Mhz possible) due to the fact that no cable exists with significant bandwidth to carry the signal.
As to the CPU, a 2500k doesn't bottleneck anything. I would recommend against 4k at this point in time not only because nothing can drive it at 60 fps, but because every one out there today will be immediately rendered "outdated" as soon as Display Port 1.3 is released and 120 Hz 4k screens arrive.
I'm on a 4k screen with a 980 Ti, and even though I'm not getting 120FPS, I'm also not playing first person shooters. 4K is insanely better looking than 1080P, and unless some one is twitch gaming, there's no need to go 120FPS, yes, that would be ideal, but this isn't an ideal world, and just because 1.3 DP is coming, it's not here yet, and will take time to implement, so, OP can go 4K now and enjoy what is a great looking experience at playable frame rates, or wait another 2 - 3 years, *maybe* longer, for cards that can push 120FPS @ 4K. BUT 8K tvs are all ready out, he should definitely wait for that as that will be the bomb, course, that's another 5 or 6 years before video cards that can push that at 60FPS, but what's a few years if you need the absolute best experience.