I tested restoring by extracting the compressed, custom-format backup to a plain text SQL script¹. This is much faster than restoring to DB, while still testing whether the archive is valid. For the most recent backup, I also tested restoring it on my local machine, which takes ~50 min². (Backing up takes ~25 min³.)

¹ make backups/public.<date>.backup/test &
Note that the compressed format is 9x smaller than plain text: 7.5 GB for all backups vs. 67.5 GB (75 GB - 7.5 GB after all were extracted)

² make backups/public.2012-07-12-13-34-33.backup/restore & :

     3048.69 real        25.65 user         7.26 sys

³ make schemas/public.2012-07-12-13-34-33.backup & :

1508.94user 26.71system 25:57.51elapsed 98%CPU (0avgtext+0avgdata 38256maxresident)k
3448inputs+2220544outputs (57major+6427minor)pagefaults 0swaps