Jason said: "Trail runners would most likely be next on the tier which are best if the load carried is around 15lbs. on an established trail."

I'd suggest this as a personal rule, and not one that's universally applicable --- for me, that seems like quite a low weight threshold (i.e., implied is "if over 15 pounds go to boots").

I got to know a lot of PCT thru-hikers this year and most of us were in trail runners, and we mostly carried over 15 pounds for most of the distance. In the Sierras this year my pack weight was over 40 pounds in places and there's no way I would have wanted to trade for the extra weight and the slower dry-out time of boots over trail runners.

It's not just a matter of thru's being stronger, more up-to-speed either. When I'm out of shape and doing a weekend trip, I'll still take trail runners.

It seems that most especially with footware that each person has to try out different options and work out what's best for them.