ORIGINAL: Tired Old Man
If the ignition is set at 28-30 btdc, do not retard the ignition. Your engine performs best when spark timing works in conjunction with port timing. The gas octane has no effect here. The higher octane delays detonation, but only effectively in high compression engines. Trust that you do not have a high compression engine.
Higher octane always delays detonation and tuned pipe setups need a little more octane to prevent predetonation/knocking. I'll tach the engine next time I'm out. It sounded like it had more power, if it's the same I'll go back to 89 octane gas.