Yes, I’m aware of that. My feeling was that at 180% performance was OK, but on further testing it does carry a penalty. I tested again just now, and at 180% the desktop was perceptibly slower, although much less than the last time. For example, at the first run there was no unusual CPU usage, then the second time virtualbox was using maybe half a core just to keep the display updated. Anyway, from now on I’ll use 200%.
Now I’m trying to deal with the real tiny fonts on some native java apps. Their size seem to be hardcoded. There is still some way to go to make 4K work OOTB on openSUSE. Perhaps when Wayland goes mainstream (if ever) 