Thanks, Richard! Very interesting.
Charles de Gaulle's ancestors were reviewed not long ago to make sure they have at least one correct source, and I noticed the McCartan connection (in its francized form, Macartan) but had not idea of the McCartan's Guinness connections - the link that might have told more of their origins is dead. Here is the earliest ancestor we have in France:
Haven't reached Ireland yet. The spelling should be Macartan for the descendants who were born in France, since that is how they are recorded in official documents.