The YS is a very good choice of engine for the mayhem, And I agree the 110 YS will out preform the saito 120 or 125 at any altitude. Don't get me wrong the Saito is avery good engine,it just does not have the out put of a YS ,there fuel delevery system really adds some HP to there engines.
Plus you can place the tank on the CG without any issues.