I am getting at least one Titan X. Maybe from Nvidia or maybe from Evga when they are permitted to start selling.
I stepped up to 1440p and sometimes that frame buffer will spike on me, even with settings pulled back. I was playing Far Cry 4 with everything turned up and that game was eating nearly 3gb of frame buffer at 1440p. I can't imagine doing 4k gaming with only 4gb.