[JimD]

It isn't really the subject of the thread but it seems the 135i gets worse mileage than the 128i regardless of the transmission. That seems logical that a more powerful engine would be worse than a less except that the added power comes by turbocharging. Turbocharging uses energy that would otherwise be wasted in the exhaust to pressurize the engine which increases it's efficiency. That is why GM is putting little 1.3 or 1.4L turbo engines in the smaller cars and Honda went to a turbo 1.5L in the Civic. These smaller turbo motors will get better mileage than the larger engine they replaced. Smaller also helps but the basic addition of turbocharging improves efficiency.

So if was geared the same, and driven the same, the 135i should get better mileage than the 128i, not worse. The torque advantage could also be used to have it turn lower rpm in top gear which would further increase it's gas mileage advantage.