bigger diamiter gives more thrust, smaller pitch gives less speed.
I ran the 12.25 prop on a sig somthin extra and it would hover it no prob, would even pull it out of a hover (5 pound plane) The speed was still respectable. on the extra easy i am not saying it is the perfect prop, it was for my SE with the pro 40. But it will slow your plane down and give you great power for takeoffs and good slow landings.