300 Wh/mile would be about right for my Ludicrous Raven X at 70 mph. I don't have a lot of pure samples, because I mostly on take pictures at the end of legs, and they tend to be contaminated by slower speed segments of road construction and heavy traffic somewhere along the way, so the average pace is substantially lower than the majority of the run.
Here's one 3 hour drive in desert summer sun that's mostly at 70 mph, with a slight altitude gain and an excursion to speeds well above anything I should admit to while passing a pack of slower traffic on a two lane road - and some stop and go on the outskirts of Vegas on the ring road they're constructing to slow it down a little:
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This one I have mixed minds about showing. It looks amazing, and did really impress me all things considered - I know my X75D wouldn't have managed it, but the basic leg speed is 80 mph in the deserts of southern Utah and the descent into Saint George causes it to look somewhat better than it really is:
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