Absolutely sure of my answer. The idea that it's "more combustible" is urban legend. Low octane fuels will combust spontaneously during the compression stroke on turbocharged, variable intake, and other high-compression engines. Higher octane fuel is formulated to retard this combustion point and thus prevent preignition - otherwise your engine would eat valves, scorch cylinder walls, and burn pistons.
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(98 S70 T5SE misc mods, mostly lighting) (92 940GLE)