FDB Restore: performance tuning and availability of parallel restore

I restored a FDB with a key-value size of 5.5TB. It took 4.5 days in our env. We are running FDB v6.2.27. Wondering if there are things helping to speed up.

I tried running multiple backup agent K8s pods to restore, but the restores would got stuck midway. Finally I settled down with one backup pod, and succeeded.

Is it possible to have more than one backup agent pod? How to choose the right number of the Backup agents?

How about the parallel backup feature? Which FDB version starts to support it? Version 6.3, or v7? And how does it improve the performance compared to what we have in FDB 6.2.27?