Wrote this a while ago elsewhere. Might be useful here.
Common idea is that higher octane fuel will give more power, but on its own this isn't true.
To start off in the early years of internal combustion engines during WW1, some aircraft engine suffered major failures for unknown reasons. One problem was found to be different fuels propensity to ignite on their own (from just pressure) without waiting for the spark plug to fire. When this happens the fuel pretty much explodes violently (rather than a slow burn). Even if only a small pocket of fuel / air explodes like this the pressure in the cylinder will rapidly increase triggering the rest to explode anyway. This explosive force will rapidly damage parts of the engine. However at the time what allowed this to happen, and how it varied between different fuels was not understood.
To classify fuels on how easily they will detonate on their own the octane rating system was devised. The octane rating of a fuel is its equivalence to a test fuel made up of a mix of iso-octane and n-heptane. If the fuel detonates as readily as a mix of 80% iso-octane and 20% n-heptane then it is said to be 80 octane. Iso-octane is very resistant to detonating while n-heptane is very prone to detonation, but the mix isn't designed to be a useful and a fuel having a high octane rating doesn't mean that the fuel contains much iso-octane.
Fuels are compared using standard single cylinder test engine with a variable compression ratio. However there are 2 main ratings which are the RON rating (Research Octane Number) and MON rating (Motor Octane Number), an the difference between these is in the details of how the test is performed. For the RON rating the test engine is run at 60rpm with an inlet temperature of 52 degree centigrade, while for the MON rating the engine is run at 900rpm with an inlet temperature of 149 degree centigrade. Also the test for the MON rating uses fixed ignition timing while for the RON rating it is varied. The 2 ratings for the same fuel will be different. On a rule of thumb for normal road fuels the RON rating will be about 10 higher than the MON rating for the same fuel, but this is not consistant between all fuels (hydrogen has a very high RON rating and a very low MON rating). This difference is known as the fuels sensitivity.
There is yet another system used to rate fuels and that is the RdON (road octane number), determined using actual vehicles. This will be quite difficult to measure consistently.
The USA uses the PON (Pump Octane Number). This is merely the average of the RON and MON ratings for the same fuel. This apparently reflects fairly closely with the RdON and so is probably more meaningful for a road vehicle.
What this does mean is that US PON ratings and European RON ratings are not directly comparable. The same fuel will probably be said to have a 5 point higher octane rating in Europe than the US.
Fuels that have an octane rating of over 100 are tested and their resistance compared with extrapolated results for the normal control fuels.
Note that none of these tests make any differentiation between the power of any engine when run on these fuels. Generally a higher octane fuel will need more energy to ignite, and will often release less energy when burned. You can easily have a fuel that has a very high octane rating but releases very little energy creating very little power (methanol is a bit like that, although it compensates by allowing a very rich mixture to be usefully used). Indeed a slow burning fuel is likely to have a high octane rating.
A normal petrol engine is not perfect. It relies on the fuel burning, but how much effect that fuel has will depend on the piston position at the moment it is burning. If the piston is at top dead centre then no matter how much force the burning mixture apples to the piston at that exact moment it can't push the piston down short of bending the con rod. Similarly when the piston is at bottom dead centre any last bits of mixture burning are wasted. When the connecting rod is making a certain angle with the crankshaft then the burning mixture can apply the maximum turning effect. As the mixture takes a certain time to burn the engine wants the time when the most mixture is burning to correspond with the moment when the crankshaft can take the most advantage of it. With normal fuels this means igniting the fuel before the piston reaches top dead centre, giving the flame front time to spread for maximum effect. If you advance the ignition timing you gain in this way, but you also have the mixture burning (increasing its volume) at the same time as the piston is still trying to compress it, and as the pressure increases the chances are that some of the unburnt mixture will have been compressed enough to spontaneously explode (resulting in detonation and probable engine damage). Thus having a fuel which is less prone to spontaneously explode (ie, a fuel with a higher octane rating) enables the ignition timing to be safely advanced and it is this change that gives a bit more power. Changing the fuel alone without changing the timing to take account of it means no benefit.
Similarly with compression ratios. The more the mixture is compressed the more energy that is released when it is burnt. However again if the mixture is compressed more then it is more likely to spontaneously explode. A higher octane fuel allows a higher compression ratio to be safely used.
As you can't really adjust the compression ratio while riding / driving you can't safely use a lower octane fuel once you have raised the compression ratio for more power. What you can do is retard the ignition timing (losing you power) to make it safe to use a low octane fuel once you have raised the compression ratio. It would be entirely possible to raise the compression ratio to gain power from using a higher octane fuel but then lose even more power by retarding the ignition timing to cope with the fuel you were previously using.
Some ignition / injection systems use knock sensors (although very few bike ones). These are basically a microphone which can pick up the noise of the exploding mixture with detonation compared to the normal noise of a burning mixture. The ECU can recognise this and then change things to remove the problem, probably by automatically retarding the ignition timing.
Supercharged engines (either mechanical superchargers or exhaust driven turbo chargers) have extra things to play with. A supercharger will push more mixture into the engine and this will give more problems with detonation. However the boost pressure can be fairly easily changed, so if a high octane fuel is being used the ECU will up the boost to generate more power until knock is detected, and then back off a touch. With supercharged engines quite a lot more power can be generated from using more boost, hence a higher octane fuel can give a substantial (or at least quite noticeable) increase in power if the ECU can adjust the boost to take advantage of it.
I hope this has explained things a bit, and hopefully shown why a higher octane fuel on its own won't give any more power unless things are adjusted to take advantage of it.
All the best