Hobbsy, were those Bolly props the carbob fibre (black) ones or the baby poo yellow clubman series. If the carbon fibre, I use the 13.5x6 on my duration model powered by a YS 63 are they are very good, make sure you balance them well though and check for voids (there has been an odd report or 2 about this (carbon fibre) though I have neve experienced it myself.