More efficient Mail backup scripts for Tiger server?

I've written a script that handles performing nightly backups of my mail server, rolling the backups, compressing them, etc. Currently it calls mailbak.sh (with a few minor fixes) to do the actual stopping of the mail services and performing a full backup (to a staging directory on a second volume) at o'dark hundred (mailbak.sh syntax: "mailback -b path_to_backup_directory -p"). Unfortunately, it's currently taking about 2¹/₂ hours to complete.Resulting nightly backup archives (compressed w/bz2) are 5+GB. I've used mailbfr a couple of times for moving mail configurations (another question regarding that shortly in another thread) and it's seemed reasonable and maybe even a little faster. My assumption is that I could then also let mailbfr do its incremental backups to the same staging directory to improve the backup speed, correct? What are others using and what are your experiences? Would switching my script over to use mailbfr be a better choice? Has anyone run into issues with letting mailbfr do its incremental backups for long periods of time (i.e. do you have to blow away the staging directory once a week/month/etc to make sure it's reliable)? Thanks for any feedback.