The 46 is a slightly better plane after trying a ST.51 I ended up with a Tower .60 on it. One thing with a UCD any size, if the nose is not pointed up, using more than 1/2 to 3/4 throttle will blow apart the plane with flutter. It is a tough plane but it is not a high speed plane. You need a 90 2 stroke min. for the 60. Fuel milage goes up because you dont need to be at full throttle.