It depends more on your flying style combined with the airplane. Personally I don't go for speed but on some planes I do like vertical. On scale models I usually don't over power but some scale planes need weight in the front so I would choose a heavy motor. With a long nose moment I would pick the lightest motor even if its a little less powerful. I am planning to build a Zlin and think the Saito 100 would be perfect because of light weight. Currently I'm building a Mitsubishi Claude and it has a very short nose so I will make a dummy radial to surround the Saito 180. This might add a pound to the front which will be needed. I'm not interested in over powering these models. I want to get a DPM Ultimate and plan to but a Webra 120 in it which should get the plane going very well.

You can over power models but if you use the throttle and stay close to the recommends you will be fine. Spend some time thinking about how you fly and want you want the plane to do. Put-put all the way to 3D.

Carl