I wore the heavy weight kilt on a hike uptown, so I gave it a good workout. To be truthful it wasn't as hot as I would have thought. While sitting in a diner with the kids it was a little more blanket-like on my lap than the 13 oz, but I wasn't being tortured to any extent. Sitting in the sun or in a car might be a different story entirely. I am of the belief that what we wear up top has the most to do with how warm or cool we are. I was wearing a very thin cotton shirt and no hat.
I'll second that blanket type feeling while sitting. I have a Medium weight kilt. Which at the moment is VeryHot to wear.Far to warm for a hike in the woods so I've used shorts recently.( Alright I'm sorry )

I'm thinking of a 4 or 5 yarder in a lightweight next to get more use in the hot weather.(Then maybe I can go for a little more kilted time. There that better now )

Also I'd like to say you have covered the subject very comprehensively.I look forward to your winter repot.How cold does it get where you live