Contributor to the PG bulk loading docs you referenced here. Good survey of the techniques here. I've done a good bit of this trying to speed up loading the Open Street Map database. Presentation at https://www.youtube.com/watch?v=BCMnu7xay2Y for my last public update. Since then the advance of hardware, GIS improvements in PG15, and osm2pgsql adopting their middle-way-node-index-id-shift technique (makes the largest but rarely used index 1/32 the size) have gotten my times to load the planet set below 4 hours.

One suggestion aimed at the author here: some of your experiments are taking out WAL writing in a sort of indirect way, using pg_bulkload and COPY. There's one thing you could try that wasn't documented yet when my buddy Craig Ringer wrote the SO post you linked to: you can just turn off the WAL in the configuration. Yes, you will lose the tables in progress if there's a crash, and when things run for weeks those happen. With time scale data, it's not hard to structure the loading so you'll only lose the last chunk of work when that happens. WAL data isn't really necessary for bulk loading. Crash, clean up the right edge of the loaded data, start back up.

Here's the full set of postgresql.conf settings I run to disable the WAL and other overhead:

wal_level = minimal max_wal_senders = 0 synchronous_commit = off fsync = off full_page_writes = off autovacuum = off checkpoint_timeout = 60min

Finally, when loading in big chunks, to keep the vacuum work down I'd normally turn off autovac as above then issue periodic VACUUM FREEZE commands running behind the currently loading date partition. (Talking normal PG here) That skips some work of the intermediate step the database normally frets about where new transactions are written but not visible to everyone yet.