Paul
I forgot to say that I have Murphy relatives in Antrim (Broughshane) who were Presbyterian as far back as about 1800. They must have been Catholic at some stage and are likely to have become "soup kitchen Protestant" - changed religion to get a job under the penal laws or even just to get some food during a famine. perhaps your Antrim McCauleys wetre originally gallowglasses fallen on similar hard times.
I also forgot to mention that I discovered Nancy and Isabella McAuley in the PRONI will indexes and will be trying to find them on the microfilms (not easy) on next visit to PRONI in July.
I assume you know by the way thet the Irish National Archive has started putting the 1911 and 1901 censuses on line, in that order. They have done Dublin 1911 and are moving on to Kerry then Antrim/Down (inc Belfast I imagine). It's all at a snails pace however. Dublin has been available for 4 or 5 months but no progress since then. Link
http://www.census.nationalarchives.ie/best wishes
David