Re: the 30GB update size, probably worth saying that I've heard from several reliable sources that after the update has been downloaded and applied the final size of the Odyssey game installation actually goes DOWN by about 6GB. One possible explanation for this (which ties in with reports of siginificantly improved framerates at settlements) is that FD have converted the game's textures to a smaller and/or more efficient format, which could easily affect a large number of the already installed game files and requires a significant number of them to be downloaded again and patched.
I have to say, if there's any truth in these rumours then it's really bizarre that FD wouldn't mention it - a) because improving framerates would be a massive thing to shout about in the patch notes and b) because it would address all the damaging speculation and expectation surrounding what the additional 30GB could mean.
The game didn't get smaller. I still have the U17 asset directory (\Win64), which, sans logs, is 99%+ of the game*. If someone's install is going down in size, something else is being removed. A 6GB reduction sounds like someone accidentally deleted a year or two's worth of netlogs.
I haven't see
any changes to performance yet either. I haven't tested CZs yet, but the tutorials and other settlements are well within margin of error.
* specifically, U17 patch 1 was 89,466 files with a total of 55,369,878,864 bytes, while U18 is 90,821 files and 55,706,915,815 bytes total.