It’s been a while since I tested it (pre-Wayland). The main problems I saw back then was that the window managers tended to do lots of file I/O for things like moving windows or opening menus so it was critical to tune the I/O scheduler (and NFS home directories were game over), and since rendering was up to the app it was common to have, say, the chrome respond relatively well but everything inside the window would be chunky on the main thread.

I’d hope this is much better now given things like Wayland and the increased use of parallelism.