[joshbaptiste]

Test data

  josh@snoopy:~/Downloads $ dd if=/dev/zero of=test bs=1024K count=1000
  
  josh@snoopy:~/Downloads $ gzip -l test.gz 
  compressed        uncompressed  ratio   uncompressed_name
  1176024          1048576000  99.9% test.txt

with -p2 it runs ~2 sec slower

[alecco]

For that kind of data you can just use RLE instead. It's the trivial case (an edge case in fact).