I just finished the GP Master and stuck the MDS 68 in mine.{{The only MDS engine I have been able to get to run correctly}} So far I have only flown the plane once so I don't have A lot of answers about it.
The engine is plenty, the loops were very big with no sign of being under powered at all.
I only put the ailerons on the bottom but have A servo for each one. I think it could use ailerons on both wings because the roll rate was on the sluggish side and not very snappy at all.
The instructions said the rudder responce was almost nill at low speeds so I enlarged it quite A bit and rudder control on mine is great at all speeds, even when landing.
The only real problem I have seen at this time is when landing, it's A floater and doesn't drop when I try to just use throttle control. The only other Master I have seen and flown was the same way.
When I got it home I added A little down and right thrust to the engine but as yet haven't got to fly it again so don't know if that helped with the small trim problems I have with the normal ground handling and little aileron trim I had to add for level flight. It wanted to drop the right wing in flight and it liked to wander to the left on take off.
When I fly it again I will post up on how it flies now with these slight trims.