I'm currently on hiatus from building a Contender. I've chosen the ST .51 for mine. My theory is to build it as light as possible and use a forty-sized motor. What I mean by "forty-sized" is that many engine makers have several different engine displacements available in the same case size. For example, the ST .51 is the same case as the ST .40 and .45. The plus is that the bored motors will produce more power swinging more prop (albeit burning more fuel) than their smaller counterparts.

So if you like my theory, other motors that would fit this criteria are...

Irvine .53
MVVS .49
Webra .55
GMS .47
Magnum XLS .52
J'En .57

Now for the ultimate example of more displacement and power in a smaller case size, the Jett .60 is actually the same outer dimensions as his .40. It is supposed to be an awesome motor. (I have Jett racing engines and can say that Dub produces nothing but the highest quality items. In addition, his customer service is absolutely second to none.)

Now, if I owned a Jett .60, I wouldn't choose to put it on the Contender. That motor belongs on a more appropriate plane.