<< Higher Octane can def. increase performance! >>
If that is the only variable, that is a patently false statement.
ShadowHunter either had a 'heavy foot' after the fillup or something was amiss in the engine. It had ZERO to do with the gas if the remaining gas in the tank wasn't polluted with water or impuritys that might have been impeding proper running.
There are very few differences in gas regardless of the brand. They meet a particular standard and ANY ingredient added is controlled by the Government. There are no secrets in gasoline formulation.
To simplify it, the octane rating's only effect is in it's resistance to detonation. Detonation,or pre-ignition as it is sometimes called, occurs when the fuel-air mixture in the cylinder 'explodes' instead of burns. The pressure increase in the cylinder caused by higher compression by design or carbon buildup possibly,cause the mixture to ignite before it is supposed to. Advanceing the timing too far has the same effect. You can heardetonation. It sound like someone rattleing marbles around in a coffee can when the car accelerates.
If there is no detonation and the car is in tune you are wasteing your mone on a higher octane blend.
In gasoline engines the mixture must burn at a controled rate. In diesel engines the fuel explodes by design. That is why you hear that signature rattle of a diesel.