FWIW, I was running a minimal 6.0.8 from a 800K floppy in the MacPlus until this morning (computer just died -- see other post).

The Mac SE/30 is running 7.0.x off a 2GB internal HD.

I tried running earlier SW on the Plus, but really, I didn't do much with it and 6.0.8 did what I needed it to do and fit on an 800K floppy, so that is what I used.