That's a big heavy boat to be downgrading power on and the 50 hp per engine decrease will affect both cruise/speeds and top end as well as acceleration. Stay with the higher horsepower and torque of the 425Hp version. My suggestion would be to use the ECM's you already have as buying used or new ones or having the old ones re-programmed is moderate to expensive and cams are not that expensive other than the replacement cost.
We have good cams in stock that are actually better performing than the GM stock HO camshaft. Call us @ (866)496-8181 if you are interested in that option.
Ray @ Raylar