proxmox backup slow

I have just replaced our backup server with a Dell machine running a pair of 8 core Xeon Gold 6144's with 512GB of RAM, and 24 x 12G 7.68TB SAS SSD's in a hardware RAID 10 on a Dell PERC H740P (I have tested ZFS as well via HBA mode). The PBS box has a pair of 40Gb NIC's in a LACP to our Nexus...