in reply to
Curve fitting for rsync snapshot deletion
Rereading your post, I will ask this (for completeness)-have you looked over what is being backed up to be sure you are not backing up unnecessary files (cache/temp files, installers/ISOs/other large files you have elsewhere, etc.)? Also, does your backup include things that may be changing frequently (example: database files, Outlook .ost/.pst files, etc.) that may result in changes/updates causing the entire file to be archived multiple times?
Just a thought.