The Mike Tyson of the backup world - VCB
So It took a bit too long to get right, but VCB is a powerful tool to get your backups flying along.
Network congestions, poorly configured ports, old servers, all other known enemies of the Backup guys/gals are defeated with the move to Virtual Servers, and the use of VCB backups.
Our setup is around 40 vm's and the strategy was get the oldest boxes that cant be decommed over to a VM. Now boxes that would jam up our backup window are leading the pack. We get speeds regularly around 45,000KB /Second. This was a game changer in our environment, and with the incrimental backups now available I have no issues at all. The other nice factor that helps our stats is the lack of partial backups. It's an all or nothing game, and once you get it right, you have very few failures. If you do have one its a snap shot jam up most of the time. This is fixed quickly by logging onto your vmware infrastructure client, and deleting the VCB snap thats sitting there.
My suggestion is give it a try and see how fast a windows backup can be.