The hardware we have running our SAP implementation far surpasses anything else on our legacy systems so to try to compare wouldn't be fair.
I can tell you that we can get anywhere from 80 to close to 300 gb/hr throughput on a backup. Which is nice when you are backing up 1/2 tb db's in under 2 hours.
The restore process appears fine if it is on disc, however I believe if we had to pull something from tape it would be a quite lengthy process...
I am not sure regarding your last question, The only way we have been able to do backup and restores (at least the only access we have been granted) has been to do the backup in CommVault and restore to another server). If the files are on disc vs. tape then the process is pretty slick and pretty fast IMO. I recently had to restore a db from tape, and it was a very slow process.
As far as are retention policy on disc we are still working on that, currently we are trying to have 2 cycles on disc (14 days) for production.