I wouldn't be too concerned about what airfoil used as long as the percentage numbers are in the ball park. What I have done is played around with the tip airfoil having it's high point a few percent further forward then the root. Reason being is a more forgiving wing at low speeds. That part seems to be working but it ended up taking a little more effort to get clean breaks for snaps and spin entries. Properly done, a foam wing can be lighter then a built up one. The secret to that is careful wood selection. Use medium balsa on the high point, contest grade at leading edge and trailing edge, bond with epoxy and vacuum bag.