short answer...more horse power. I'm not being sarcastic.
I have a 24' , twin 25" tubes, 115 hp CT motor.
I have used a merc. 4-14x14, 3-16x12, 3-16x13 and a current solas 3-15.5x13...
The 4 blade merc, 3-16x13, and solas 3-15.5x13 all give practically same numbers . I can post them. Max rpm is...