I flew a YT Ultimate at the weekend with a Magnum 80 fourstroke on the level it didnt seem all that powerful but when the nose went up it just carried on going. It sounded and felt good on this motor which make me feel it will do well on the YS 63 / Saito 72 / Capiche...

I agree the 13x6 is giving a little too much thrust at the bottom end.