Well I finally did it (prior to the start of 2003) and migrated from Greymatter to MT (Moveable Type). I have still to experiment further with the categories, and perhaps start a separate log for personal use with more strict security.
Looks like MT supports two types of RSS out of the box, but not RSS 2.0. This is okay for me at present.
The categories do not seem to allow for secure and insecure audiences, as all entries are archived in a single directory. Maybe archiving by category, and not individually would allow more security, but I think separate blogs with web server security per directory will be required.