5
I had to manually change some table names for some modules and manually add and rename some fields in a couple of module tables, but apart from that, the upgrade went smooth from e-xoops to XOOPS 2.0.10 - just by using the normal installer at /install/index.php.
I'm making no guarantees, though - I have as mentioned absolutely no idea, which version I upgraded from.
"When you can flatten entire cities at a whim, a tendency towards quiet reflection and seeing-things-from-the-other-fellow's-point-of-view is seldom necessary."
Cusix Software