I'm running Zimbra OS Edition, version 5.0.20, on Debian 4 (Etch).

I'll upgrade Zimbra to the new 6.0.x branch, using the Debian 4 version.

My question is, how should I proceed to upgrade the entire system to Debian 5?

Should I start from scratch and restore a backup after everything is installed?
Should I dist-upgrade my Debian install and then install the Debian 5 Zimbra packages?
Or should I install the Debian 5 Zimbra packges and after that dist-upgrade to Debian 5?

Is there any documented procedure?