Hi Dan,
I hope your local authorities decide to give you real broadband in the near future, however. :-)
My situation is similar to Darren's: My primary connection to the internet is through my cell phone carrier and a mobile WiFi hot spot.
I'm UK mainland, get about 580 KiB/s download, and pay per byte during the day, which is why I try and get most package updates during the toll-free midnight hours, but sometimes I need a new package and can't delay.
My vote, whether it has any weight or not, is for higher compression ratios at the expense of CPU cycles when decompressing; i.e., xz rather than zstd.
I'd also favour fewer bytes, but would suggest replacing xz with lzip as xz has quite a few flaws in its file format. Xz format inadequate for long-term archiving https://www.nongnu.org/lzip/xz_inadequate.html https://www.nongnu.org/lzip/lzip_benchmark.html#xz compares the two in various ways, and explains how xz's -9 allocates double the dictionary memory than lzma's and lzip's -9 and thus initially looks better unless the playing field is levelled. -- Cheers, Ralph.