What is the client attempting to accomplish? Four LTO3s is a lot of
bandwidth for six servers. The biggest problem with modern tape drives
is that they can be somewhat unreliable when they are run at less than
full speed. The ability to properly utilize the tape drives depends as
much on the servers being backed up as the interconnect used.

We have done some installs using a disk based virtual tape library
(VTL) to handle the initial backup streams and then replicated to a
tape library. This allows inital backup to be completed as fast as the
servers can provide the data and then the tape drives can be driven as
fast as they can handle.