i know the m-pro cam is a single cam but when you look at alot of the arrow selection charts they ask if you have single ,hard ,medium or soft or round wheel. what would be the correct one to choose for the m-pro cam? also when they ask for arrow lenght they list 27 and 28 inch shafts,well if you shoot 27.5 inch arrows ,what do you use for the lenghth,27 or 28?