I've done some tests in the past (but I have to search for my results ...).

Note that these are with 100 Mbs Ethernet.

Recent ones:

Exchange TDP
Exchange DB compressed 50.3 GB - 1:19:30 elapsed time, 10.81 MB/sec (Backup)
Exchange DB uncompressed 63.1 GB - 1:36:30 elapsed time, 11.15 MB/sec
(Backup)

We backup Oracle directly with the b/a client, (No TDP) and always get huge
compressions rates (88% compression).

This was a multi-session backup test a while ago:

(Again on 100 Mbs Ethernet), 9.9GB of source data (compressed to 1.19GB)
elapsed time of 152 seconds - this translates to 65 MB/sec which we could
not achieve with 100 Mbs Ethernet without the compression.  (We tend to max
out on CPU on these types of backups).

With client compression on backups you have to make sure no files are
growing during compression and being resent - this will add time to your
backups.  We exclude files like .zip etc from compression and also scan the
client logs for any files that grow during compression (you can also use
compressalways to avoid the resends).

I'm going to search for other tests I've done (or do some again) and I'll
post those results.

Tim Rushforth
City of Winnipeg