I would expect up to the maximum available from Exchange (27GByte per hour),
depending on the network performance - say 24 GBytes per hour or so....

Estimates based on a test of NT Exchange Server to NT ADSM Server at 100 Mbs
Full duplex and nothing else on the network. This achieved 23.5 GByte/hour
with no particular ADSM tuning parameters set.

The Exchange Connect agent acts as a "large file" pipe - so there is little
ADSM database access as the Exchange database is backed up.

Cheers, Chris