I can't say i've been testing with PB sizes, but for my "meager" 8TB backup, Borg works well. A daily backup & prune operation takes less than 20 minutes.

Restic falls over as soon as you cross 2TB sizes, and prune operations are painfully slow. Backing up 8TB took 4 weeks with Restic, and i gave up waiting for prune to finish. It was crossing the 24 hour mark, making it unsuitable for daily backups.