the rate of backups can be influenced by things like IOPS and Port Speeds and Network of course - but, if none of those are an issue, the "normal" items still come into play.
our system is designed for 2 things
1) to backup servers, even the heaviest servers with as minimal impact to those servers as possible (ClusterLogics is very well documented and understood to have the smallest impact on devices being backed up amongst any other backup software)
2) in case of disaster, to BMR servers as quickly as possible (it accommodates this by passing large groups/blocks of files during a BMR)
if your network and IOPS and Ports are not an issue, once can achieve 30-80% port saturation during a BMR
backups however are not meant to operate like a BMR - backup speed (assuming iops, network and ports are all NOT presenting bottlenecks) is determined by # of files, whether or not you compress the data before backing it up, what types of files you are backing up at different times in the backup process (ie mysql or web files) and size of the individual files you are backing up