I'm not running a 4K display on my laptop but a QHD+ HiDPI display (with a resolution of 3200x1800).

I've settled on Debian Jessie(testing) with the Cinnamon desktop environment and Opera Beta as my web-browser, it all works perfectly and the clarity is wonderful and couldn't imagine ever using a non-HiDPI screen again.

It's absolutely terrible. I have used 4K and 5K displays in the last year on Windows, OS X, and Linux and the only OS that currently handles these well is OS X.

In general, handling high resolution displays requires a really tightly bound ecosystem so scaling works on all applications. Linux makes it immediately clear what happens when this is not the case. 14.04 is totally unusable because you have to either change the system fonts to be huge or scale text within every application individually, if the application even provides the ability to do that at all.

The latest version of Gnome, 1.4, detects high res displays out of the box and scales everything automatically (except for applications that don't use GTK3, like Chrome, but Firefox with the Gnome theme scales well).

Tried Hi res on a Dell M3800, Gnome works well, kde doesn't, and for programs, chrome does not render well. I don't know for other programs