To add to hardware that's being mentioned in this discussion, for reference, I use a 27" 4k monitor (Dell P2715Q) at 1.5x scaling and a laptop with 15" 4k scree

To add to hardware that's being mentioned in this discussion, for reference, I use a 27" 4k monitor (Dell P2715Q) at 1.5x scaling and a laptop with 15" 4k screen (Dell XPS 15 9550) at 2x scaling. Both on Arch, X11, and just a window manager (currently Xmonad, but just before that StumpWM and i3, too). One of the reasons being I prefer to have direct control over Xresources, xinitrc, etc. to set up dpi, color management, etc.