Gentlemen, it turns out the initial part of an apt-get update, the part which sends GET /debian/dists/unstable/InRelease HTTP/1.1 Host: ... Connection: keep-alive Cache-Control: no-cache Pragma: no-cache User-Agent: Debian APT-HTTP/1.3 (0.8.15.5) (as seen in tcpflow(1)), does not get a compressed result. Even though it is only a 150 KB reply, but why not enable compression and just send a third of that?
We do not have any support for compressed replies (only for replies containing compressed files, ending in a compressor-specific file extension), adding that would need a lot of work for not much gain. Yes, we can go down from currently ~ 200 KiB to 61 KiB, but I don't think that's going to be a huge advantage.