V-ray best number of vADP streams per datastore ?

Wondered if somebody had some best practice regarding number of vADP streams per datastore

All I have been able to find in Symantec documents is that you use more than one stream to saturate the backup path, which in our case is 2x 4 Gbps SAN connections to the media

Netbackup 7.5.0.5

VMWARE vsphere 5.1.0 update 1 on ESX hosts and vsphere 5.1.0 on VI Center