both are likely to underpower the thing. the asp 61 would have a little more power, but they both really lack the power to pull it around nicely.see, if you want to progress, a bit more power is desirable because you want to have the ability to add a bunch of power when you get into trouble because unlike the trainer, they will stall out and power is the only tyhing that can help you there. you can be the best flyer in the world but recovering from a very dangerous situation without much power is not always possible. if you don't want a bunch of power but want enough to do the required tasks and have enough to save you, go with the os 91 surpass. it is a good engine. it ain't a real stump puller of an engine, but it is very reliable, stingy on fuel, and fires right up. it weighs the same as the 70 because it is the same case.