When the Ringmaster Jr was relatively new, Ihad a Green Head Torp 15 that weighed about three ounces on one that flew at a very high rate of speed with a 7/6 prop, and I used an 8/3 instead to slow it down. Years later, I put that engine in a Jr. Streak, and it was too fast once again (for anything but combat practice). I filled the mount holes with stubs of dowel, and redrilled it for the 15X of the day (so-called "steelfin"), which with an 8/4, was matched up just right.

I also flew the Jr Streak with a Medallion 09, with which is was moderately fast (actually, I didn't fly it much. It was built for my son, age 6 at the time). We had a Baby Streak about the same time, powered by a couple of different Atwood 049s, and it was a very good flier.

I would imagine that expanding the Baby while retaining its light constrction, will be a very nice plane.