I can only offer you this. The human genome is ~3Gbp long, or 6Gbits. Luckily, I have a copy (HGP output!) stashed away somewhere...
% cat ./NCBI/DNAinput*[^x] | gzip -c > /home/ariels/abc.gz
% gzip -l /home/ariels/abc.gz
compressed uncompr. ratio uncompressed_name
875526472 2940172494 70.2% ../../abc
Which is really pathetic. Even accounting for various housekeeping information we store in the files (apart from the genomic sequence), I'd expect to manage 25% at least (the amount for straightforward 2-bit per bp scrunching).
bzip2 doesn't do much better -- it gives a compressed size of 803381365bytes, for a ratio of ~72.7% -- still less than the minimal decent ratio of 75%!