Also, a person's height, or more importantly, the length of their femur, comes into play when describing Range of Motion. Im 6ft 3, and my ROM (well the actual distance travelled throughout the movement instead of the degree of the angle) going parallel would be greater than a guy whos 5ft 3 and doing the same depth. Also, the taller you are, the greater the stress on your knee tendons, (and also causing more of a pronounced pelvis tuck and subsequent back rounding), the deeper you go. I, and many guys who are tall, can attest to this. As a final note, Sumo Squats, like Sumo Deadlifts, are easier on my knees, and other guys who have long legs do not experience knee pain in this stance.