I tried a 50" UltraHD, and trying to get it to work properly was a big waste of time for me. The issue was connectivity -- it simply wasn't ready -- the existing standards didn't have the bandwidth and/or are at best hacks. I don't think the situation is much better now.
I wouldn't attempt UltraHD again until next-generation connectivity options (such as DisplayPort 1.3 or USB Type C) are in the channel. (USB Type C looks particularly nice -- a single cable type for basically everything, including UltraHD.) And I also wouldn't retry it until monitor/graphics card/OS combo's have been qualified by someone else, preferably the monitor and/or graphics card companies themselves.