What are you backing up to? It sounds as if you are using re-writable CD/DVDs.
You would be far better using an external drive; preferably a fairly fast one. Breaking your data into smaller files would also help. There is no need to keep backing up data that doesn`t change; so perhaps you could back this up separately and avoid it when you do your full backup.
In my opinion ATI is the best backup tool available, but to get the best from it you need to use it efficiently and with the best media.