I forgot to mention that my experimentation was with the AC on the latter half of the trip, and it's impact was barely noticed.
Consider that the AC simply can't sap as much power from the motor if rpms are low. Most AC compressors are designed to cool adequately at idle speed, and seem to run optimally just a couple hundred rpm higher than that, so any extra rpm you dump into it is pretty much wasted energy.
As a further experiment, I suggest a constant cruise rpm test of AC draw at low, mid, and high rpm. I'd be willing to bet that the losses are progressively and significantly higher with higher rpm.
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