finally! Very glad to have found this Veeam reg tweak.
8core Xeon, 32GB mem
ML6010 (8Gbps FC)
2GbE LAG to production/mgnt network
10GbE to iSCSI SAN network
10GbE to CIFS backup network
Veeam 8, 8p1 & 8u2
No matter what the source (local Perc array, 16disk iSCSI Target, CIFS dedupe appliance), performance was averaging <35MB/s rendering multiple TB backups unworkable. No joy with consistent acceptable tape library backup performance.
Until now. Reg tweak applied. Decent, consistent performance - 145+MB/s - i.e. what the LTO6 should be capable of.