Actually petrol grades are measured in Octane number, that is their resistance to knocking because of premature ignition. Engines are designed for a particular range of octane fuel. Normally everyday road cars are designed to run on average regular petrol. But in Pakistan petrol is substandard due mixing and this causes ocatne number to fall. That is why we feel a performance increase in using hi-octane. There is an easy way to find how to fil up.
Use super, if your engine knocks, start mixing some hi-octane with super. (in percentages like 10,20,30 %). When knocking stops, that is the corrrect mixture, and please do use a particular station. If you use Hi-octane beyond that, you are wasting money