There are others with a lot more knowledge on this than me, But I was in Ohio Last year and all but a few were running the Mark or Moki 2.10, I have one that I had a few flights on before I let it get too slow and tip stall on me, but I think it will repair. There is a write up this month (feb) in both Model Aviation and R C Report on the Sundowners. Some are using the YS 1.7 but it is pricy and I didn't see if they were any faster than the Moki.

Jim