Running a couple of Pis with Gentoo myself right now. It works as well as anything, although unless you’re very patient you’ll want to set up a binary package host (or distcc or something) to take the load off the Pi’s somewhat anemic processor.

One thing to keep in mind about older versions of the nvidia proprietary drivers is that they will only work with specific kernel versions (and specific X versions—not sure about Wayland). Once the driver series your card needs stops being updated, you can’t update your kernel without patching the driver. Assuming you have the skills to patch the driver, or someone who does makes their patches public.

I went through this song-and-dance with a very old laptop that had a card of the NV40 generation as its only GPU (no integrated graphics). Eventually I did install nouveau on it, and used it for several years without any issues.

Trinity Desktop Environment, forked from KDE3.

TDE has this natively under the advanced window settings, so I would expect KDE to have it too.