I'd suggest that riders almost never accurately know the percentage of the grade. Even when posted on a sign or map it is likely to be wildly inaccurate. Then there is the fact that grades are often extremely variable through out their length. So if the posted grade is correct at all, is it referring to the little 100' piece that is the maximum, the average for the whole climb, or something else. So basically any accurate grade number is unknowable in most touring situations.

As soon as you said "your loaded bicycle is 100 lbs" I said OMG. That much total weight would be unpleasant to me regardless of the pitch of the grade. I have never carried that much even on my first tour, a Trans America where I was carrying more than my share of group gear and was not that sharp about packing decisions. I'd have to have some very special reason that went well beyond normal touring to carry that much on a tour.