hi, fellow mccaig (spelling variable) when i was in elementary school, i was assigned to do a family tree.At that time, my dad said that we were somehow related to john stewart mccaig, the banker who built mccaig's tower.he was about the same age at the time as my great grandfather; they were not brothers; john stewart remained a bachelor all his life and did have a sister.
my great grandfather, arthur mccaig, and his family had moved from scotland (no area identified)to northern ireland during the 1700s when the king of england claimed northern ireland to populate with the scottish peoples.Ergo, these peoples are considered scotch- irish.
i am now researching my northern irish roots to discover my great grandfather's pedigree. i have good pedigree information from his move to america about 1860 through to the present day.
my suggestion to you is to not concentrate only on the oban area even though john stewart mccaig is a very interesting fellow, your roots may equally be in northern ireland as well.