Not sure there is any such thing as a normal backup when we are talking about NDMP compatible devices (for Backup Exec a normal backup would almost certainly usually be considered as one that uses a remote agent which never applies to NDMP NAS devices as you can't install an agent on them.
Your choices are:
1) Tape library attached to back of NDMP compatible NAS, use NDMP Option to backup
2) Tape library or disk storage device located on media server, use NDMP option to backup
3) Tape library or disk storage device located on media server, use CIFS shares to backup
yes all 3 of these will show performance differences in any single environment, but they also all have different pros and cons for other reasons. As such performance may not be the key thing you should be looking at. For instance :
NDMP backups can only be restored to NDMP devices running a similar operating system as held the orginal data.
Share level backups can be restored to more locations but can only backup what is presented via a share and will not be able to do any form of incremental backup. Share level backups will also always alert to state that the remote agent was not found.
Oh an sorry but I can't provide any performance comparison data as I don't have any
