I do not need a solution (just sharing information)
The NetBackup Backup Planning and Performance Tuning Guide, Release 7.5 and Release 7.6 is now available:
http://www.symantec.com/docs/DOC7449
This guide is for administrators who want to analyze, evaluate, and tune NetBackup performance. This manual is intended to provide guidance on questions such as the following: How big should the NetBackup master server be? How can the server be tuned for maximum performance? How many CPUs and disk or tape drives are needed? How to configure backups to run as fast as possible? How to improve recovery times? What tools can characterize or measure how NetBackup handles data?