it's slow yes, and I posted the maximum settings; as for GUIs I have no idea, never used any. for such things I prefer command line. and advzip is a command line tool. I have no idea what you actually used thenAs it works on any file with deflate compression streams, I used it on numerous kinds of them like game data files too. (think pak files in id software games) The game Torchlight has 1 deflate based data file (Don't have the name present atm - I'm typing here on my phone) advzip ran 2 days over it.
so much about "way too long"