I echo most of the responses.
Stronger internals, up the psi, improve the cooling.
I would guess that they have a reliability safety factor on their engines for certain load testing. Maybe the M branded cars have a lower factor vs the series cars but I doubt it. That said, if they increase the output of the series engine significantly like in this case, they must provide countermeasures to ensure the reliability safety factor remains constant.
That's my take anyways.
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