When I met Magico CTO last year at Munich High End show, he told me that the all ought the new S3mk3 have same 88db efficient at 4ohm like the S3mk2, the new model is easier to drive as it doesn't dip as the MK2 model.
Since I upgraded between the models last august, not changing amplification or electronic sources, I can say he was right as the new model does feel much easier to drive with the same amp's
My guess that M7, M9 are the acting in the same manner, meaning they dip less prevues generations of Magico speakers.