I think engine hours is not the whole story. If you average 50 hours a year, mostly in and out of the marina without ever getting the engine up to proper operating temp and/or idling with low or no load the engine will probably die before its time. I think an engine with more hours run more often at proper temp would be preferable to one run rarely, but with lower hours. Of course this assumes each has had proper maintenance, especially oil changes. Commercial truckers get very long life out of their diesels, seldom letting them get cold. Average marine use is just the opposite in many cases.