Hi Kitty,
yes, I do have Patrick Sinnett's branch as part of the registered surname study, as I am collecting up all references to any variant spelling worldwide in the form S-NN-T, and linking as many as possible into family trees, working with people who are also researching those different families. I think I have pretty much the same info as you - going back to Patrick Sinnett b about 1752 in Ireland. I don't have anyone from this branch who has joined the DNA project yet (at familytreeDNA.com), so if you know of a male Sinnett relative who can show a direct father-son line back to Patrick, then it would be great to get them to join the project and do a Y-DNA37 test. That may eventually help link your line to others further back in Ireland, and identify common ancestors and where Patrick came from
Feel free to contact me again if you have any other questions.
Corinne