Right, engine rpm has to be kept in the "sweet spot". For instance, even in today's automobile engines we are shooting for horsepower with lighter rotating assemblies which most often means higher rpms.....shorter strokes.....and narrower power bands with less "over the counter" torque. Of course this dictates the need for more responsive transmissions with more gearing (speeds). Often times even CVT's using variable clutching like a snowmobile. Kevlar is utilized to extend belt life and special synthetic ATF's with careful filtering is critical. The old days of poor economy, and 2, 3, and 4 speed transmissions along with broad, high engine torque, with flatter horsepower profiles.......those days are history. The 4 stroke outboards have flattened torque and horsepower curves and of course cleaned up the emissions, but when dealing with getting a heavy load on step....without ample power and torque, the prop selection, load distribution, and trim control.....all have to be properly applied together.