I'd give all ten Spock's Beard albums at least a 4 out of 5 score, but there are some songs I don't like, so they're out. Transatlantic is close, but I don't like In Held (Twas) In I much.
Gentle Giant didn't have any bad songs until The Missing Piece, so that's eight albums in a row of strong material.
Actually, I thought of an example. Proto-Kaw, a sort of Kansas spin-off band. Three albums without a dud song, IMO, plus an archival release of great demos. I'm a Kerry Livgren fanboy. But I can't think of any "perfect" bands with more than four albums.