I'm on a 12.5" laptop with a 1080p screen and a Haswell HD4400 "GPU". This does not completely fall into HiDPI but everything is just a tad too small for comfortable use on the laptop display. Because of this only highish dpi I can't use 2X scaling (not like that even works properly yet). I have selected 1.4x scaling and it helps but not enough. I have found that setting the resolution to 1600x900 using xrandr seems to deliver a perfect experience. The problem is that I can't figure out how to make that resolution persistent because KScreen does not support the resolution and reverts to 1080p when restarted.

PS. I regularly dock my laptop to 2 large 1080p monitors and then disable the laptop screen. I would like to still be able to run them at 1080p.