I have always used fanless cards over the last few years.
4K offers the advantage of a contiguous (no bezels) workspace that is equivalent to four full HD TV/monitors. I want it especially for using RX3.
However, 4K will not work on any of my video cards, and while there are several that will work at 30Hz via HDMI 1.4 connections, none have HDMI 2.0, which has the larger bandwidth for 4K at 60Hz.