RE: CG
CG has less of an impact during hover. Rear CG makes it hover more easily but less stable on other conventional maneuvers. I normally discount the impact of CG with respect to Torque Rolls. Less prop will provide less air flow on the ailerons. So you want to use a larger diameter prop. Remember you are fighting the torque of the engine so you need large aileron throw to overcome the prop rotation. Often times rudder as well, as in high positive and negative alpha flight. You will note that as you back the plane down in a torque roll it will stop spinning and may actually start to rotate to the right. Any case best of luck with your practicing.
Don