I once had a real file that gzip compressed at 100:1.
It was a list of the author's names for a large number of DNA
sequences. (Author being the head of the sequencing project
that sequenced each one.) First, they were indented about 40 spaces,
and they were done by a small number of different people.
If you make a file with a large number of the same character, gzip
will do much better than that.
-- glen