Thanks @olikraus, that eliminates U8X8 as we suspected, but U8G2 is a possible solution. I shared links to some of the 6-pixel-wide fonts in your git repo with @backintime in their other topic.
Not sure why @backintime opened a new topic for this question, it is dangerously close to cross-posting, which is against forum rules. In their mind it is a different question about tutorials, but is closely related to the same project.