Ok, here's a curve ball for ya's! I got that Larson Senza 21' with the 350 mag pushing 275hp with an Alpha One drive. The boat came with a Laser II and I've been suspecting for sometime it's not right. I just went on Mercury's website and had a good laugh when its recommended for aluminum bass boats, offshore fishing, etc..... This boat is far from that description.
My dad had on our old old boat a Vengeance, that was a Starcraft with a 350 mag also and side exit exhaust, more of a family boat being open bow... The speedo pitot **** never went above 57, there was an aluminum or whatever and that did 52, we got a 5mph gain with the vengeance.
So, do you suggest a Vengeance, Enertia, or just stick with the Laser II and screw it? Engine runs within the 4800-5200, I think to the higher side, so we probably could go to a 21 pitch Enertia, from a 19p Laser II, the problem is, the props are seemingly so different, so it would be hard for me to guess.... That's where you come in!
I know about an increase in pitch drops the rpm 100, or vice versa, usually..... I still haven't gotten a GPS, but the speedo has said 63 on near glass, this weekend we were in the high 50's, not going crazy.

Mirage+?