"Buster might find that Windows 10 on one of his old 4 GB systems is fine, for example. But it's not tolerable to me."
I understand and sympathize. But our situations are so different. I don't use just one system for everything. I have four computers set up.
My older 'slow' system is used mostly for acquiring difficult to find movies or shows, often from decades ago. Speed isn't that big a deal, and I don't need to have seven programs open at a time. It can be running while I sit by the fire or read a Regency Romance novel, a favourite genre at the moment.
My laptop, for general use is pretty quick.
My Linux system is unfortunately commandered by Marilyn, but often she does other things. Linux does some things better than Windows, and hers is really quick.
And the fourth system has 12 gig of ram. Say no more, say no more.
Different situations Jason. And I love reclaimed old computers. They like to be useful.