Sorry to dig this up, but it's the only solid lead I have in an issue I'm facing.
I'm using a Club3D adapter from DP 1.2 to HDMI 2.0 which can do UHD 60Hz. The context is: Intel i3-4160 (HD 4400 graphics), Samsung 65KS7000 TV, Ubuntu 16.04.
By default I only get the 30Hz video mode available. I used cvt to get mode lines for 3840x2160@60 both with reduced blanking and without, but when applied with xrandr, they both failed (also tried some 59Hz variants).
The only thing that worked and got me to 3840z2160@60 was the mode @nakamura specified.
My issue now is that I get a couple of flickering horizontal lines at the very bottom of the screen. Also, every now and then, the lower 1/8-ish of the screen seems to fall slightly out of sync. Is there a way to tweak that mode in order to get rid of those problems and still have the 60Hz?