the burn rate of the fuel doesn't mean it has more power or in your terms energy. Higher octane fuels use different structured molecules like branched chain hydrocarbons versus a higher percentage of straight chain hydrocarbons.
Benzene ring has 6 carbons, so pentane. Relatively speaking and definitely in low efficiency car engines, the small difference in structural changes affects available energy very little.
I doubt it affects the fuel economy at all!
Former owner of '99 CSVT - Silver #222/2760
356/334 wHP/TQ at 10psi on pump gas!
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