RON value of 87 is present in Pakistan as Super.
RON 91 is called Hi octane in Pakistan. This is regular fuel in other countries.
Mixing of RON 87(Super) and 10 litres of RON 91(Hi octane) doesnt make any difference on engine condition or mileage. Just a psychological effect. its the engine oil which makes a difference on engine condition and mileage. use a good engine oil.
If your pocket affords it, use 100% Hi octane if you want to see difference.
In Australia, its RON 91, 95 and 98.