[nine_k]

IDK, high DPI worked fine for me under Linux. I just set the desired DPI in Xfce settings, and everything scales properly. (Except Firefox, which has its own DPI setting! But it works equally painlessly.)

Where things go haywire is mixed resolution. It's best avoided :-\ Hence now I have a 28" 4k external screen which is exactly like four 14" FHD screens of my laptop, so the DPI stays strictly the same.

[clhodapp]

Mixed resolution can look great on X11 if you do it with super-sampling, especially if you're able to do it via integer downscaling.

[pxc]

> Hence now I have a 28" 4k external screen which is exactly like four 14" FHD screens of my laptop, so the DPI stays strictly the same.

I did the same and just bought monitors that all have the same DPI, so I can easily use scaling that matches on all of them.