I'm running three length cranks. 165's on my touring bike. 172.5s on the full carbon road bike, and 175s on my 853 steel and carbon raod bike. the 175s are by far the easiest for me to ride. I notice no difference in ability to spin all three in the 90 to 95 rpm range. I like the 175s the best when standing while climbing. Personally, I find the difference not worth worrying about. Meaning that if there were a bike with any of the three length crankarms on it, and I liked the bike, I'd be comfortable with purchasing it. If given a choice, I'd go with the 175s.