I was reading somewhere that the BTU content gets lower the higher you go in octane rating, it's probably so negligible that it doesn't make a pissant difference, but theoretically you'll make more power by running only the amount of octane required to prevent detonation due to more BTU's per gallon of lower octane fuels.
Leaded fuel doesn't matter at all in a 2-stroke, but in a fuel injected engine it can foul up certain O2 sensors.
That reason, and emission requirements, would be the only reasons to stay away from leaded fuels.
Otherwise just save your money and run leaded fuel.
If your engine runs 100 octane, go out and buy some 100LL avgas, it's every bit as consistent as race fuel and cheaper too.
Find it at your local airport.