I am in favour of version 3 (or between 3 and 4).
Equally spaced, full-sized flats with maximal overlap. I think, saving
horizontal width is important.
I like your "intermediate 3/4 pdf".
In a very large size (your pdf 400%) they look perfect to me.
It is hard to tell with the limited resolution of a monitor, but in
usual sizes (100%) they might be too much overlapping (i.e. still moving
a little bit towards version 4 might be preferable).
Printed on paper, the pdf looks right and doesn't need less overlap to
lilypond-user mailing list