My very late contribution to this thread. Rucking with a heavy pack is much different from hiking with a light one, especially if you are pushing to maintain or improve your pace. It can really wear your hips down, especially if your belt is too low or too loose. When external packframes ruled the trails it was common knowledge that your belt should set above your hipbones. For me I have to tighten it around my belly button, let it settle, and tighten it again. With all the super light gear used today I guess it does not really matter as much, but when I start getting close to 50 lbs it becomes critical. If the belt is low it constricts the hip abductors, cuts off blood circulation, and can pinch nerves.
I train with 60 lbs most of the time because 60 is where my glutes really start feeling it. I have to constantly adjust my belt to switch the weight back and forth between my hips and shoulders. If I am going up a steep hill often I will unclasp my belt and let my shoulders take all the wait because the pressure on my hips too much.