I have a CSV that's ~30GB. Some 400m rows. Would there be a meaningful performance difference to run COPY from STDIN using: cat f.csv | psql "COPY .. FROM STDIN WITH CSV" versus just doing "COPY ... FROM 'f.csv' WITH CSV"?
If you're looking to speed up the loading - and your disk subsystem is decent - consider running your csv through the "split" command to decompose it into smaller CSV files. You can then load them in parallel using multiple psql sessions.