Oh I wholeheartedly agree that each application is different and it should be a matter of matching engine power range, intended application, and probably weight as well as airodynamic drag but who can really say how to compute all these factors on the ground. I am a firm believer in "try everything and decide what you like from there" You should have seen my gunpowder selection when I used to handload. Would have been a similar type photo to my prop collection photo.