I plugged my 23andme raw data into some other applications and viewed my Y-SNPs. 23andme just said "I1" but I was able to find P109+ with the third-party apps. I've reviewed the link you just gave and was going to refer to it in my original post but I don't have a high enough post count to post links. (in fact, I had to edit the link out of your quote) Thank you for the welcome! I am really excited to get started with genetic geneology.
I've already plugged into gedmatch, btw.
It was interesting to see how its results differed from 23andme. This is all knew to me and the wealth of information that gedmatch provides is still above my pay grade.
That's my current theory as of a few days ago. There is a tombstone in Cork for a man who lived in the 18th century who we *think* is the oldest known ancestor of my line, but we can't know for sure because we're still missing some pieces. Cork was a Viking port so it is consistent with known general history to posit that I'm descended from a Viking who made his way to Cork. Now the question is when and whether he was Danish/Swedish/Norwegian. The linked page seems to suggest that P109 was largely Danish, but I am curious to see what further Y-chromosome analysis will uncover regarding the various Norse and ultra-Norse subgroups.