Yes these are “launch” ready builds. The only difference being one is already live, Unity 5.3.8, and is on our live server and the new one, Unity 5.6.3 is on our Stage server. I can see in the console though that the load time is barely affected as all the data comes from the same cdn. It’s the “initialising” phase that takes over 2 minutes, the download and decompression takes a few seconds.
I’ve just found out too that anti-aliasing is broken in Edge Unity 5.5+ so it’s not really usable anyway.
Poking around a bit more it seems that Cloudfront doesn’t support brotli so the only option is to use gzip and set the Content-Encoding headers to gzip, that appears to load at a suitable speed on all browsers