I think leg and foot length would have the greatest impact on this. But frame size and fitting should also take some of this into consideration. My orthopedist said that while I am 6'3", I have torso measurement quite short compared to leg length. Another fellow at work drove my bus for a while as relief man, and he had the seat 6" further forward than I did. He was also 6'3", but with longer torso and shorter legs. 2 men, same height, one 175 cranks, one 160. I could actually go to 180 but they are hard to find. I was planning on doing a trainer comparison this winter, but delays to my repair of the Fuji will make that unlikely, as I think winter may break early around here. Also the so many projects, so little time thing may kick in as well.