@Wayne,
Well, if you remember, I did bother you with some PM's with different CMS and Forum software.. IIRC Invision was/is available as a module for Xoops, but it could also be another CMS. (Not saying you didn't reply, you did ;-))
At work we dropped the idea of using a CMS, as we only "need" a forum, we decided to get a forum based on SQL, not MySql, and also dropping PHP (.net / ASP). Not sure about the name of the (free) package we are using now, but is it a consideration to drop MySQL ? Sure, nothing wrong with MySQL.
Also to consider, Xoops is free, MySQL is free. SQL and Invision are not.