Porsche wrote that any certified oil for use in their engines is equal to any other certified oil.
Certified being the key. Not "meets or exceeds".
Both the m1 0w-40 and castrol 0w-40 carry the a40 Porsche certification. So Porsche says they are equal.
One can believe one is better than the other but the truth of the matter is any m difference in formulation is irrelevant.
They are functionally equal. Buy the less expensive one
Porsche wrote that any certified oil for use in their engines is equal to any other certified oil.
Certified being the key. Not "meets or exceeds".
Both the m1 0w-40 and castrol 0w-40 carry the a40 Porsche certification. So Porsche says they are equal.
One can believe one is better than the other but the truth of the matter is any m difference in formulation is irrelevant.
They are functionally equal. Buy the less expensive one
That is completely incorrect. Both carry the certification meaning that both are "good enough" for porsche. That in no way implies that one is not better than the other. One could very well exceed Porsche's requirements by more than the other.