Having additional interfaces will provide failover connectivity, but likely not present more performance. Most users will put the AltaVault interfaces into a VIF (virtual interface, 802.3ad).
To address your 5.1 comment, the read throughput is to show that there was no bottleneck on the client side (aka the 4 linux systems could deliver in excess of capacity over the network to AltaVault). In this case, they could deliver in excess of 2.9GB/s, which is greater than 1.5GB/s (which is the translation from 5.5TB/hr) to AltaVault. Again, these are examples from synthetic workload testing of data sent to AltaVault.
Regards,
Christopher