One other thing, is configuring a storage node with backups run at the 
location ( you will need someone to do tape management) an viable option 
for you ?
When and if you have successful backups, how long does it take and why 
does backup fail on other occasion, besides using latest networker client 
you should investigate whether or not any QOS policy over wan can be 
applies which may prioritize backup traffic between specific hr ( always a 
hard sell).
How about doing differential backups during the week ?
I am just giving you all the options, some may not be completely suitable 
for you.

HTH

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