Performance tuning keys for VMware backups and restores
If you are looking at tuning performance of your backups generally, recommend you to go through the Backup Exec 2012 performance tuning guide:
The actual size of the write operation during a backup job can be verified using Procmon. Filter the output of Procmon to entries from beremote.exe with writefile operations with the details column showing the actual length of the write operation. Additionally the VMWare Agent backups can be debugged.