HI,
Please, take a look at
Backup Exec 2012 Tuning and Performance Guide
http://www.symantec.com/docs/DOC5481
Performance issues there are most of the times related to enviroment issues, believe me when I told you that I had an issue once with performance where the backup were running too slow and it was due a faulty UTP wire. :S
Also, if you are using deduplication (I'm not an expert on that option) take a look on the following documention, I know that option requires some specific hardware:
Media Server Deduplication and PureDisk Performance Requirements
http://www.symantec.com/docs/TECH156743
That technote is for NBU, but had some point like:
Media Server Deduplication and PureDisk (with or without PDDO) in some environments seem to perform much slower than expected
1. Possible issues involved are using a single large LUN presented from the SAN with multiple disks in the same Column.
2. Possible switch, cable or SAN issues.
3. Make sure that all components (mainboard for the system, HBA, switch, and SAN) are running the latest firmware that may have possible fixes for the issues being experience
and etc, etc...
Hope it helps,
Bye!