People tend to gut air boxes all the time, then wonder why their engine hesitates, lean pops through the intake, stalls, falls on it's face and eats pistons.
By the time you recalibrate the carburetor to compensate for the extra air you'll be lucky to achieve an additional 25RPM and perhaps .000001MPH top speed.
Just remove some weight from your boat is the easiest way to increase top speed, run less fuel in your tank and the result will be similar (nearly imperceptible).