A little further up, I mentioned that the warmer air can increase efficiency. Please allow me to clarify - or to write what I should have written!

Most people talk about colder air being denser, and hence being more efficient. However, our engines are power limited by the fuel pump settings - they are still running with a large excess of air when they begin to smoke.

The meaningful efficiency gain that is open to us is the reduction in pumping losses which the warmer air gives.