As many have mentioned above, they cannot stay on plane below 4000K, ideally a boat should be able to get on plane before its ideal operating rpm, most outboards are between 3400-4000, being at the high end will not necessarily harm the engine, but yes sometimes these heavy boats do go through outboards quicker, but not always. What it does mean is when the seas get nasty you need to maintain a high rpm to stay on plane and cut seas, otherwise you will take a pounding, having some rpm to slow down and stay on plane is good. If you are climbing nasty seas, you want to be able to pull off the throttle and then punch it to stay on top of waves, if you are already running at a higher rpm, you have less power to punch it and stay on top. I'd say a 250 minimum, and ideally you want twins for that boat. Another alternative is a repower with a 300 Suzuki, many on here have done so and are pleased with it.