If for example you have the Perk Lightweight which lets you run faster, through challenges (how far you've run in this case) you can unlock Lightweight Pro. But even at that point there are additional challenges (I, II, III, etc.) at further and further distances. These provide experience bonuses, but do they also confer any game bonus? If you have completed all levels of a given Perk, are you any better with it than if you simply had the Pro level?