The zlib fork with "massive performance improvements" appears to perform worse than the earlier and actively developed zlib performance patch set from Intel [1]. Why start from scratch?
I noticed they had a zlib fork as well. The Zlib team (mark adler?) hasn't merged in the intel patches as far as I know. Maybe someone needs to make some kind of official fork of zlib, development on it seems to be stalled.
[1] https://github.com/jtkukunas/zlib