BuddyPress.org

Hi all,
I know there’s a plugin for external authentication. Yes I am not sure if we would be able to use it in this case. Let me describe what we want to do:
1. External database that stores contact information including login and hashed password.
2. Local (by local I mean the buddypress one) that has all the post/replies/friendship requests/status updates etc etc information.

Is is better to try and make WordPress authenticate in external database directly (SugarCRM in this case), no entry would be created in local db, and then somewhat attach that login and contact details to user in local db (wordpress/buddypress). My concern in this case is, how would buddypress know that x user in sugarcrm posted y and z on buddypress.
or would it be easier and safer to synchronize databases e.g. every couple of minutes?
So in the second scenario, all the information is created locally (wordpress) and sychronized with SugarCRM.