Hi Andres
OK yes, you can't use SAN Transport because of the RDM (in case of VMware type backup) or SAN Client (because its a VM and doesn't have its own FC).
I'd start with reducing the streams and then increasing them again to see where you get the best performance. That will take a few backup runs to figure it out.
I suppose you're running 10G so the network shouldn't be the problem. You can monitor the client's read performance during the backup, and see at what stage it maxes out.
Example
1 stream provides ± 40MBps
2 streams provide ± 80MBps
3 streams provide ± 120MBps
4 streams provide ± 120 MBps <<<<You'll see at some stage that it doesn't help to add more streams. It just loads the processor / memory but there is no incremental improvement in transfer speed.
Any chance to migrate from RDM to VMDK would make your life easier ;)