Ok, so all on one box:
-Backup the 4.5.6/.10 on debian 4 with 3.1 binaries
-Upgrade it to 4.5.11 on debian 4 with 3.1 binaries using the same
How to install Zimbra Debian 3.1 binaries on Debian Etch 4.0 [Workaround]
-Backup the 4.5.11 on debian 4 with 3.1 binaries to a safe/offserver location
-Remove your current /opt/zimbra (backed up to a safe location)
-Install 4.5.11 using the -s flag with the debian 4 binaries
-Move the rsync or whatever the /opt/zimbra directory backup into place.
-Run the normal installer
-Make sure GID's & UID's still match & run zmfixperms as needed if you didn't keep attributes on your backup process.
-Make sure every thing's working & take another backup (so you don't have to do this all over again if the v5 upgrade fails).
-Upgrade to 5.0.5
Good luck!