I probably should have stopped reading and posting to this thread long ago as it only made me question my conclusion that the 11" is the better option for me (and waste more time unnecessarily). LOL But yesterday I borrowed a relative's 12.9" iPad for the afternoon and spent some more time with it just to revisit the issue.
There are a few things I love about the 12.9" -- the bigger screen is great for video and I really like that it has the numbers row on the keyboard rather than having to switch back and forth when typing on screen. I also think the speakers are a bit better, but while both are good, neither compares to decent headphones or an external speaker(s). Split screen for my use isn't a big deal and honestly I felt like a 50/50 split generally left both screens too small anyway. On the other side, I still felt that it was just slightly bigger/heavier than I prefer and I didn't have the desire to just grab it and look something up quickly or maybe do a bit of surfing on the couch, etc. YMMV
I really wanted to go for the big screen and I suspect there will be times that I wish I had it. But the choice was put into perspective when my wife suggested that perhaps it made sense to get the 12.9" and then buy the regular 9.7" 2018 iPad to take to work/commute, more casual use, etc. I told her that didn't make much sense because I would wind up using the the regular/smaller iPad 90% of the time and would have spent a lot of money on the 12.9" for not much use. I still use my 27" iMac most of the time at home and I don't see having a 12.9" iPad changing that. I still watch movies at home on my Television and I don't see my iPad changing that either. And, as I've mentioned before, I must use my work issued laptop for office and out of office work.
So, I think I answered my own question. It looks like the 11" it continues to be. (I wish I could say the matter is completely resolved, but I will undoubtedly still think about it until my return period is up at the end of next week

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As has been pointed out, the choice is extremely subjective and the decision for each person comes down to a set of variables that are very specific to that individual, including their particular use, physical size, other devices owned/used, budget and not least important, personal feelings about preferring a larger vs. smaller device.