I have two AS/400s running as two different ADSM servers, and have seen similar
results.  What I have seen for performance is similar, on very large files I can
get as much as 5Gig per hour throughput, however, on our data server which most
files are word documents, excel spreadsheets, things like that I have seen
poorer performance...more like 3.5 Gig per hour.  Also keep in mind that this is
regarding performance on full backups, incremental can be very different.  Here
is a example from one of our clients

NT Server
approx. 870,00 files
approx. 3 gig/day changed
total DASD used approx. 132 Gig
62.2 Gig used
Incremental takes from 5:30 am to 9:15 AM

I have found that with large number of files, the comparison of files is what
takes the large amount of time...but that during full backups the network IS the
bottleneck.  Keep in mind that even a 100 Mb switched network can only push
about 4-5 Gig/hour through before it is at capacity.  If you are doing the math
right now, keep in mind that ethernet networks do not work well when beyond 50%
capacity.

Rob