There is no permutation that I have yet found of window manager / display manager, that correctly scales windows and applications on two different monitors with two different DPIs.
I have a 40 inch 4k monitor running about 110 dpi, plugged into a hidpi Dell notebook at about 240dpi. I have to accept far too tiny assets on the hidpi or far too large on the big monitor. It just doesn't look good. Yes there are some "halfway points" that kinda work, and Unity does allow asset scaling separately by monitor to some degree, but I still get problems in applications themselves.
I have tried different combinations of Unity / Gnome 3 / KDE / I3 and even e17. Most of the time display manager (I think) was lightdm, as the distro was usually Ubuntu, but I have tried Fedora 22 also, and Kubuntu which I think use different display managers. Very latest versions each time / clean installs.
All of the time I'm seeing poor scaling effects. I don't mind running beta software. I don't mind some instability. What I do mind is visual inconsistency. Where should I go? Which distro does this well, now?
I'd ideally like all the window manager components and the applications to scale consistency.
Should I wait for Wayland? Can I get it now? Does that solve the problem?