We already know the performance difference between Turbos and N/A, but is it true that Turbocharged engines, while presumably more complex than naturally aspirated engines, are actually more efficient? What exactly defines efficiency in this case, the factors? from internal and structural standpoint, which engines are more long-lasting, durable and reliable?

Let me pose some examples. BMW's S65 V8 in the E9X M3 and the newer S55 twin turbo I6 in F8X M3 and M4. Which of the two would be the more durable, reliable engine, the more efficient regardless of what EPA says?

Or howabout this. Ford's awesome Coyote 5.0L against the 3.5L Ecoboost in the F-150. Same questions apply.

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Or even Merc's AMG turbo engines against their natural counterparts?