>The solution cannot be to use more powerfull clients.

Hmm.  Given that, and whereas it takes 10x longer for the client to
do backups with compression than without, does your client backup
log show retries with compression?  I'm wondering if it's something
like having COMPRESSAlways No in effect and the files already being
compressed such that the expand in client compression and the
transaction has to be repeated?  There should be some indication in
your logs as to why this behavior is occurring.  If not, consider
activating client tracing for a sample job.

  Richard Sims, BU