uniquely identify mv objects

In ILM 2007 implementation with only a one way synchronization of users and contacts from AD to ADAM, we uniquely identified MV objects based on anchor (cn and dn attributes for that record in AD) along with another custom attribute.

Now in ILM "2" RC evaluation I am exploring provisioning of new users and contacts from multiple authoritative data sources, and re-thinking ways to uniquely identify MV objects for searches, joins etc. I was thinking of using objectGUID and/or objectSID in conjunction with cn and a custom attribute. Any thoughts?

Thanks.