Comment # 16 on bug 98333 from Daniel J Blueman

I am experiencing the same 4K @ 30Hz limit with my RX460 and LG 27UD88-W
monitor via a Highspeed HDMI cable. I have enabled HDMI DeepColour on the
monitor, needed for the monitor to advertise 4K @ 60Hz.

Kernel is stock 4.9.11 on ElementaryOS (Ubuntu 16.04) with the HWE stack.