Adobe now allows users to use the GPU to speed this up in the Develop Module, if you have a powerful enough GPU. Please read
Some people still report problems; others indicate it works properly.
The speed issues aside. Which sounds like maybe a whole nother issue. I was referring to the scaling issue. That the interface elements are so small on high res displays (4K, QHD etc) that they're unusable.
I 2nd this. I too have the CC Photoshop/Lightroom running on a Dell 27" 4k Display along with two Acer 23" (1920x1080) and I have to rely on the Acer to read my menu items and such. The panels seem to scale "ok" however the rest of it hurts my eyes. The picture though is gorgeous, but I refuse to run to a smaller monitor for the main panel window to read the menu.
I'm going to be buying a 2nd 27" Dell to match so I don't need two 23" on top of each other, but the only way I can make that work is if I run Lightroom or Photoshop on one monitor at 4K and one at a lesser resolution, which defeats the purpose of buying a 4K monitor for photography editing in the first place.
"The panels seem to scale "ok" however the rest of it hurts my eyes. "
I have the same problem on 32" 4k Display (win10, LR-CC, RX 460 Graphics, i7-4790)
AND if there is scaleing on, the filemenue at "Katlog export" will show not all posibilitis at the bottom.
(at 200% you can only see half tof he first checkmark).
My work around: for this operation (Katalog export) i set scale=100% (i can nothing read) but i can set the checkmarks and set scale back to 200%. So i can read the side-panels but menu is unreadable smal. i learned to use the keyboard
ADOBE please fix this issue!