Can't answer that without knowing what boat you are running it on. But it is safe to say that the 10 x 13 is the standard prop shipped with the motor. They were pretty good at fitting the motors with the best prop for the average boat the motor was likely to be used on. Unless you have a very light/fast boat, or a heavy one, or are pulling heavy loads, you probably are ok. The only sure way to find out is to run it with the normal loads with a tachometer to check the RPMs.
