I posted while back about changing my prop i have a 1974 70hp evinrude with currently a 14x16 prop. It tachs 5400rpm book says 5000rpm wot. I was going to change to a 14 x 17 but i was looking at them and most are 13 1/4 not 14? If i go to 13 1/4 would i lose speed or gain? What difference would...