RE: Differential
Nobody has ever suggested to me that differential was desirable on a 424 or 428 and I have asked a couple of top racers. In theory differential would result in less induced drag as a result of roll input. The drag coming from the increased left from the upward moving wing (down aileron) and adverse yaw from the increased drag from that same wing. Kind of a clumsy explanation sorry but just trying to keep it short.
Denis