I know but figuring that Meduims are more muscular it would make sense. like a light could go faster and the meduim have more power while the heavy is just to heavy bur can like heave him self up stuff.
When you're climbing, you either want to have lots of muscles to move lots of weight, or you don't want lots of muscles which don't have to move lots of weight. It's really just a matter of perspective.
However, when you have less weight, it's easier to perform such things as wall-hops.