For me, I can really feel the difference when I go over 30 pounds.

I'm fine with anything under that, but anything over it feels heavy and it hurts. I tested loading different combos of gear a lot last season and even before putting it on a scale I could always tell when I went over that mark.

Like the proverbial "straw that broke the camels back" I suspect that we all have a weight that marks our limit like that.