im 5 8 and have the 178's the go to my forehead. and im same weight as you. i love these skis, i came off a 169 fujas. and i can tell you that there isnt much difference at all from a 171-178. measure out 7cm, its basically nothing man, especialy with center mounts, just go with the 178. you will grow into them trust me. im somebody who has seen both lengths, and im basically same body type, and im realy happy with the 178's. hope this helps