As Alec said, parkour is a very individual discipline, and therefore the question of the "perfect height" isn't the correct question. Intuition suggests that taller folk may have an easier time with tall passe murailles, while shorter people may be able to navigate underbars more easily. Of course, height is just one of a myriad of factors, along with weight, body composition, muscular strength and distribution, skill, diet, and so forth, that determines a person's optimal ways of movement. Just know your own body, capitalize on your strengths, minimize your weaknesses, and train hard and safe.
