why would you ride a 159 if you're 120lbs+...? that seems retarded. i'm 5'10 160lbs and i ride a 153cm. my friend is 6'0 200lbs and rides a 153cm, both gnu boards which are made by the same company as lib-tech.
if you're 5'10 160lbs 156 is okay but you could easily ride a 152. it might even be better, because im assuming you want to do park with that banana.