I think Volfy is in the right way.

Resume: The engine needs an octane ratio. If you use a lower one, you wil destroy the engine (a hole in the piston is very common). If you use and higher one, you will not get more power but it will not harm. There is a posible benefit: if the aditive to get more octane ratio is the "plumb tetraethil" (In spanish: Tetraetileno de plomo), as this is a good lubricant, the engine runs smoother.

What we have to understand is that wwe don't have tod think about octane, but "efective compresion", which is not the same as compresion ratio.
Efective compresion is just what it means, in the combustion camber. Enginers design the engines with a concrete efective compresion, based, over all, on the compresion ratio, and the diferents types de gas available. The more the efective compresion, the biggfer the power obtained, but there are limits: preignition.

Once the engine is designed, the gas octane is fixed from manufacturer, in which it will work well.

So, if the engine is designed for 90 octane, you wil not get more perfomance with higher octane ratio, only spend more money. But if you use 85 octane, it is posible there will be preignition problems.

Once the octane ratio is selected, you can "play" with the ingnition point, advancing it at full throtle, untill it preignite in orden to get top power. There is a problem advancing timming: as you advance the ignition point, it is more dificult to start, because the spark fires before it is necesary.

To solve this problem, you need and electronic ignition module with auto advance, or a linkage with throtle arm wchich moves the sensor, or a retard starter, as the CH Electronics do.
Resume: The engine needs an octane ratio. If you use a lower one, you wil destroy the engine (a hole in the piston is very common). If you use and higher one, you will not get more power but it will not harm. There is a posible benefit: if the aditive to get more octane ratio is the "plumb tetraethil" (In spanish: Tetraetileno de plomo), as this is a good lubricant, the engine runs smoother. If the aditive is the Methil ter butil ether (MTBE) or similar there is no advantage.

All the above are de basis, in acordance with our "little" engines. In other engines like motorbykes, cars, trucks, boats, what happens is they are more sofisticated, and incorporate electronic ignition, depresion retarded ignition, preingition and predetonation sensors, etc, which set the timining point. The only way to get more power in theese engines with higher octane, is if such one was using a lower one it needs, and the preignition sensor was retarding constinuously the ingnition advance to avoid preignition.

I hope this helps you.