Seems some folks here dont understand octane rating. I am no master mind on the subject of octane, but its commen sense that higher octane wont mean more hp for all engines, especially a stocker with low compression.
BTW @MacDizzle, the reason for the tick was because your engine didnt like the Heptane percentage in your lower octane. Higher octane such as 91 means 91% isooctane and 9% heptane (Heptane is the zero point of the octane rating scale. It is undesirable in petrol, because it burns explosively, causing engine knocking, as opposed to branched-chain octane isomers, which burn more slowly and give better performance.)
So the higher the octane the less heptane. BUT heptane also acts as a solevant and thats why you want the lowest possible octane your car requires.
To the OP, yes, I +1 that for SOME people, lower octane is better for specific cars that dont require the higher octane (Higher octane ratings correlate to higher activation energies: This being the amount of applied energy required to initiate combustion. Since higher octane fuels have higher activation energy requirements, it is less likely that a given compression will cause uncontrolled ignition, otherwise known as autoignition or detonation.)
BTW, in parenthesis is str8 form wikipedia.