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I think peak torque has a lot more to do with peak volumetric efficiency rather than peak efficiency period.
I'm not 100% sure on this but peak thermal efficiency rpm is mainly friction/cooling and sometimes combustion efficiency. Higher rpms always mean more friction, but higher rpms always mean less cooling loss because the burning charge has less time to cool as it expands. In addition, since the intake air is moving faster at higher rpm the charge is more homogeneous and burns better.
But by far the most important factor in BSFC is load, because decreasing load means you're spending more of your engine output to overcome friction and throttling losses.
Anyways Mulder25 the reason you have less torque in a higher gear is not because the torque available at a lower rpm is significantly lower, but because in a higher gear you have less torque multiplication to the wheels. I don't think starting in 2nd will save gas because if you start in first, you spend less time slipping the clutch, but shifting to 5th at 30mph is a good idea. As long as you're using the available power in a lower gear, it's okay to use that lower gear.
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