GM shows peak horsepower at 4600 rpm on their website for the Mag, but that could change slightly with the Merc exhaust manifolds. I don't think you'll want to go much higher than what you have (4700), since the power curve falls off pretty fast at higher rpm.

Michael

I dyno tested one last year. Peak HP was at 4700 RPM, however it only made 5 HP less at 4500 RPM. So between 4500 and 4700 would be perfect. Prop for about 4800 with a light load and cool weather, then you'll be around 4500-4600 with a full load in the boat during the summer.

for a mag range is 4400-4800 rpm limiter cuts in at 4950. You should prop it so that in your best conditions, light on fuel, cold air, no extra weight, you are close to the 4950 mark, that way in the real world you will be able to get close to 4800 regularly which is what you want.