John;

  I think you are best served performing a search of the "Stunt Design" sub-forum.  These topics and a host of others (e.g. stabilizer/elevator thickness relative to wing thickness) have been discussed therein.

r/
Dave

Subscribing.

Thicker airfoils produce more lift & drag than thin airfoils.  Since stunters want to go slow & turn tight, a really fat airfoil is good.

Speed, racing, and carrier just want to go fast & don't need to turn, so thin is good.

Combat is a compromise between speed & turning.

Keep in mind that the flap is PART of the airfoil, (moving part).
When you count thickness in % , you MUST count the fixed part + flap together.
Finally the achievable Cy (lift coefficient) depends not only on the thickness, but the camber appeared by deflected flap, the attack angle (alpha), radius of leading edge and several others...
Cx (drag coefficient) depends mostly on the thickness.

The turning ability of model is another question...