High octane fuel in itself will not add more power. As HeadSmess said, it just burns slower which is why ultra high rpm engines (like Formula 1 engines) use octane ratings that are almost the same as pump fuel, because the duration of the power stroke is so time limited; necessitating a faster burning fuel.
In our 2-stroke Chinese engines, it pays to use the highest octane (non ethanol) pump grade fuel because oil in the fuel reduces octane rating and also the standard CDI uses an advance curve that is excessively advanced for a 2-stroke engine; leading to detonation problems which consequently hammers out connecting rod bearings. A high octane fuel in this situation helps to manage detonation.
Another factor which HeadSmess alluded to is the notion of fuel octane being related to the desired rpm range you choose to run at.
If you are setting up your engine to operate in the lower rpm range, where good lugging power is desired, it pays to use the highest octane fuel to avoid low rpm detonation issues.
At the end of the day, in real world operation, you are not going to be excessively disadvantaged by running high octane fuel in a low compression Chinese 2-stroke engine and for the low fuel consumption of these engines, the extra cost of (ethanol free) high octane pump grade fuel is negligible.