The only thing I will say about compression is that the I6 motors come with very un-inspired chamber designs that barely avoided detonation on 1966 Leaded gasoline, but in a boat with endless supplies of cool lake water, you should be able to bump your compression to 9.5 as long as you have a steady supply of premium fuel.... which most marinas don't have
Once you factor in that a 1-point increase in compression is usually good for 10% more power.... then consider that increasing your hp by ten will probably only net you about 1-2 mph, it may not be worth the headache.
You also can't really add much more cam for two reasons: 1) shifting the the torque curve up in the RPMs is a recipe for sluggish planing, or (in extreme examples) no planing at all. It can also superheat exhaust valves if you are cruising below the torque peak's RPM. 2) with a wet exhaust, additional valve overlap can cause water reversion which can cause some bad stuff.
My suggestion is to go with more cubes. The term "cubes are king" is never more applicable than on the water.