I wouldn't run them parallel.
The settings, for one, have changed quite a lot since 5.39c - lots of new options in the CP. Not sure how the UBB would behave if there were no values to the settings (as opposed to the features turned off - not quite the same thing!)
You could make a COPY of the data to test things though.. Just don't run two live boards against the same data if they're not the same version.
Oh, and FYI, I don't think licensing would be an issue - I've always interpreted the license agreement to mean live boards (development/test installations over a short period of time don't count IMO). However, I will ask Infopop to post a short statement on the issue.
Graeme
