Help with Parallel operation in Donation Copy

[stg]

Hi, after donating I got this Donation Copy to download that has Parallel operation.

I am looking to speed up my backups and think this would work but need help to understand it a bit better in what Parallel actual means.
On my home network I have 7 PC (Me, wife,kids etc) and all data is on a Buffalo 1 Bay NAS which contain a 3Tb data drive. I also have another Buffalo 1 Bay NAS that runs as a backup to the data drive.

I also have a 2Tb dive on my PC that I use as a additional backup device.

I used to just use batch xcopy for my backups but I found FFS and donated.

So the time is quite consuming at backing up (5 hours), so looking to speed things up overnight and read about Parallel operation. Do I just increase the parallel count up to 2 for each drive or do I put 3 or 4 etc or keep it at 1?

So, here is a better description of my setup.
Data Drive - Buffalo 3Tb NAS on 1Gbit network connection.
Backup Drive - Buffalo 3Tb NAS on 1Gbit network connection.
My PC 2Tb Backup Drive (SATA III) on 1Gbit network connection.

My FFS backups is...
Data Drive NAS to Backup Drive NAS
Backup Drive NAS to My PC Backup Drive.

Thank you for reading and hopefully helping.

[Zenju]

https://freefilesync.org/manual.php?topic=performance