Hot Rod tested the theory several years ago with the then-new oxygenated fuels mandated by the EPA. Once the test engine reached its limit for spark advance and mixture enrichment, the less volatile fuel (higher octane) lost horsepower across the board.

It was more of an issue BITD, when combustion chamber design was more cut-and-try. Now, with modern designs informed by 50 years of intense research, smaller chambers that burn quickly and direct injection that gets the liquid fuel rapidly atomized with minimal loss, it is common to see muscle car era static CRs that are quite happy on 87 octane pump regular unleaded. Anything more than the pump premium is largely un-necessary.

From my POV, even though the 'experts' claim my 1987 GM 305 TPI should not care about the octane, when I splash a tank of 92-93 with a gallon of CAM2 100 unleaded, the spark advance irolls up to the max, and that ol' Bird just singsa, or s my father often said, "like a ball bearing on a surface plate."