Hello. Could someone please share some advice about a propeller I am looking for? First let me state that all I want is top maximum speed. I have an Evinrude 125 in good working order. I have found that with a 13 3/8x17 prop, I hit about 45mph topped out at 5500 rpm, then I tried on a 12 3/4x21 which was apparently too much pitch because my motor would only turn 4500 rpms. What would you suggest as a good prop for max speed 13X19? The boat is an 18' Kona fiberglass, 1970, and the motor runs at 4500-5500 rpms. I have heard that each pitch size reduces rpm's by 200. Is this true? Thanks 