hi,
besides other helpfull answers,
you may want to check how quickly your client can create small files.
Write a script which creates  974008 files in a directory tree in temp
directory and watch.
This can be a bottleneck as well.

If neither this nor network is bottleneck,
then tape seeks will probably be.
In this case you could plan $$ for a disk based primary backup storage pool
;-)
at least for small files (you can have small files landing on disk STG 
while large ones  bypassing it and going to tape)

regards
Juraj