RE: RCV Engines
I think that there are a number of factors to consider. The size and shape of the cowl, the type of plane, sport or scale, and the type of flying would be the most likely contributors.
For me, the two biggest things the SP has for it is the narrow profile, and the large prop. These are important for a scale subject.
For a sport plane, the CD with it's low head and conventional prop size/rpm would probably be the better choice.
Scott