FWIW, I recompressed the jemplode.jar that comes with 2.0b13 with zip -9 and I got an additional 1.5kB reduction, but then zipping that reduced it by about another 150kB. This is likely because it it much more efficient to compress one big file than multiple small ones, which is how zip works, unfortunately. It does provide for much easier random access to the archived files, though.