This is admittedly a bit OT, but I was just curious: Why do people refer to Android as if it was a distinct OS from Linux? To me that's like saying "I use SUSE OS" or something. Just a pet peave of mine. It's not as if it's a new OS. It's a variant of Linux just like countless other variants of Linux that we call Linux.
You've got the volumetric efficiency relative to rpm part backwards. Volumetric efficiency goes down with rpm. Thermal losses go up as surface area of cylinder goes up. However, pumping losses etc go up with rpm. So, the most efficient engine is one that is able to produce the most torque out of the smallest displacement. Or in other words, run at the lowest rpm to meet application's power needs. This is what lies at the heart of why you see in countries where fuel is more expensive than in the US the majority of cars sold are turbocharged diesel engines even though these engines are much more expensive to make than gasoline engines -- they get high power at low rpm the way large engines do but have lower surface area in cylinders). In other words, they are large engines stuffed into small displacement using positive pressure induction and high compression ratio. Another example would be how, if you have a manual transmission car, you'll notice that operating at higher rpms exponentially decreases mpg. A corvette with almost twice the power of a car like a Honda S2000 will actually get better gas mileage in any conditions where the drivers are using the full power of the vehicles (eg racing of course but even just driving them like sports cars are designed to be driven on mountain roads or whatever).