I would give you the best advice I can give... Don't overthink it.
Find a boat you like and take care of it. It will last you a long time. Trying to base your choice on a brand decision or a low/high rpm will have you still shopping 10 years from now. I am sure we can all state examples of every scenario of engine life, but the reality is that there are no rules that govern engine longevity. Please don't drive yourself crazy trying to prove the impossible because there is more to a boat than just the engine.
And besides, by your description of future use, it will take you many, many decades to come anywhere near the point-of-failure you are trying to predict.
Go find yourself a well cared for boat that fits your lifestyle. Period. You will be a lot happier!