That's super interesting I have never heard or thought of that. I wonder how that compares to tilting your head back slightly to get the same eye:monitor angle?

This is all getting into personal preference, but AFAIK, ergonomic standards do not exactly recommend eye level, they recommend that looking in a straight line you should see over top of edge of the monitor. There's definitely some tradeoffs to be had as having the monitor too low can put stress on your neck (which translates to neck pain after a while).

That's gonna really depend on the monitor, of course. My 46" 4K, that'd be on the floor. :-) But, I've had pretty good luck with keeping my monitors lower, and I tend to have issues with dry eyes.

That sounds reasonable. What I've seen from various websites, and enjoy from personal experience, is having the top of the monitor at, or slightly above, eye level.