burns
OWG
For highway mileage, the leaner you run the better mileage you will get. That may not be true in situations where you're doing a lot of shifting.
I'd have to see some evidence before I accept that as fact.
I suspect there is a point of diminishing returns since a leaner mixture will require less spark advance which could well result in lower effeciency. And of course mileage drops off drastically once you melt a hole in your piston.