My VW Cabrio (A/T) gets its highest continuous MPG from the lowest RPM I can maintain in its top gear. That's somewhere around TPS 7 to 10 and 1600RPM on the flats, which puts me in the high 30s/low 40s for speed.
You didn't ask about "practical."
I understand that other vehicle/engine/transmission combos have different profiles and it can be possible to rev too slowly and hurt FE. If you're trying to work out what's best for
your vehicle and you can't test it directly, try to get input from someone else driving the same model, or as close as possible.
Hope that helps,
Rick
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