Great stuff. I was taking notes as you were going through and you answered pretty much all the questions I had written down.
I expected to hear you mention SAC dies, but because of that I was surprised at ~55:30 to hear you haven't tried their comparators. The variability I can measure in the openings of the Hornady/ Stoney Point gauges really made me question their utility for setting up a sizing die, especially after getting a Whidden comparator that came with one of their dies which was cut significantly better.
One SAC video specifically got me to buy in on their gauges was how they will match the shoulder angle that's cut into their bodies to the cartridge versus the single contact point on the Hornady and Whidden inserts. Combined with the 3* angle on the bullet comparators, I bit the bullet and got a kit. I'm not 100% sure this is correct, but one of their headspace comparator inserts is a "primer base" that's I assume is something with a hole cut so that you can measure a case with the primer seated, fired or unfired.
I had to stop for the night at 1:04 so if you discussed this in the last 20 mins... oops.