I had a similar issue when running BE 2010 (https://www-secure.symantec.com/connect/forums/bac...), which was resolved by a WAN optimizer, unfortunatley even at full speed we didn't have the bandwidth to make our window so the project was scrapped0. Fast foward to today, we've since upgraded to BE 2012 and are looking to reimplement the off-site DR now that we've upgraded the WAN link between our two primary sites (Chicago/Houston) to 100mb.
This time, even using a WAN optimizer, I get extremely crawling speeds when trying to do a backup with B2D (via UNC path to off-site host) or RMAL (via NDMP to off-site RMAL host with virutal tape drive). I'm talking about 100MB/min, or about 5-10mbps when monitoring the WAN link. No performance changes with or without the WAN optimizer in place.
I've also tried to use the B2D test tool, which does some backup simulations with 4GB test data, but it crawls even slower.
NTBackup, SCP, SFTP, Windows File Transfer between the same source/destination server are all able to fill the pipe @ about 80-90mbps, but not BE. There is little to be done in terms of customization with BE so I'm not sure what I can try.
Any ideas?