Originally posted by "Mr 2"
Typically racing gasoline's actually burn cooler and require less fuel to burn efficient. Basically if you are running fine without detonation then there is no need for race gas.
You will probably lose power by adding race gas without leaning your car out a little because of the cooler burn.
Think of octane as a rating of how well the fuel resists combustion.
Its a two edge sword since high octanes will help during high pressure and temperatures scenarios by inhibiting unintended combustion but that inhibition will also work against motors with pressures and temperatures that do not require that octane.
That is the reason for the lower burn temps since it slows down the combustion rates and why you might need to lean out a mix of high octane fuel.
The bottom line is use whatever minimum octane your engine's circumstances require.
I would imagine your reliatively stock b16a with 10.5:1 compression can live just fine with 91 octane.