You may be able to raise the motor for a little more rpm, ideally you need 5500 Rpm. Your boat weighs 800-lbs. (42 mph is not bad). Would only gain maybe 1 or 2 mph. Just my opinion, not an expert. I would leave it alone though your not that far off from max Rpm as it is.
Laissez les bons temps rouler!
Let the good times roll!