If you want the airplane to fly exactly the same upright as inverted then the wing and stab should be in the same reference plane. That way the downwash in either upright or inverted flight is the same and the downwash is a strong contributor to the horizontal tail effectiveness. Having the inline wing and tail condition will cause all maneuvers will be more symmetrical with the same control inputs. Having the wing in a horizontal axis through the center of mass of the airplane will help keep the rolls axial, etc. For example the CAP has the low wing and high stab which makes it pretty bad compared to the other two airplanes mentioned.

That being said if you lay the planforms over each other you'll probably find them all to be very close to each other - close enough to the point that indeed power to weight becomes the predominate factor. Well sorta - you also need a light wing loading to go with it. Putting a hugh heavy motor in the front of a small light airplane won't make it fly OK. A look over the airplanes that are being used at places like XFC indicate what are good setups to use.

Having a good pilot will help a less than capable airplane but a good pilot given the choice will pick the best airplane to win the XFC (try to remove the effects of sponsored pilots, etc.)

I personally don't care for the CAP but I have seen it flown beautifully by a lot of people. I should admit I had a very heavy CAP that would try to snap roll whenever I gave it too much elevator throw. I gave it away.....

Ben