Do NOT buy any 4K display. I have the Sharp that is sold by Apple as the display for my new MacPro and it only works at 30Hz. The result is an unstable finder where the mousepoint is huding a lot.
Aplle says they kniw if the problem and are workung on a solution..........!
It is a software thing. The monitor us fine but Apple software sucks.
Wait for the 4K that will bear the Apple logo.