You can use desktop manager to either do a "device switch" which would port over all your data (aand maybe applications) or you can do a backup of the data from the 8300 and then do an Advanced restore to the 85xx selecting only the data that you want to restore.
I recommend the switch device wizard as it also updates your pin in BBMessenger if you use that. That way all your contacts get updated with your new pin.
I backed up my 8300, unplugged it, plugged in my 8530, restarted Desktop manager. went to Advanced, and opened my backup file. The Address Book file is grayed out, so I can't restore it.