Why waste your money on higher octane? The engine is programmed for 87 in the US. I do not know about other countries. If it is programmed for 87 you will not gain power or mileage with higher octane. Sometimes it will even decrease mileage. Car and Driver magazine did a test a few years ago on a Honda Accord designed for 87 and it did worse on 91. Now if it is designed for 91 then you will get more power from 91 and if you use 87 the computer will adjust the timing etc to produce less power and eliminate knocking.
Further to my previous post, I've be reading up but only to get very confused. However, the bottom line is different methods are used to calculate the octane rating, which accounts for differences between the USA, UK, Australia and Asia. I suppose the best thing is to follow the factory specification nominated in your Owner's Manual/Fuel cap for your country.
The only grades available here are 87,89 and 93. I used 93 for over six months and averaged about 22mpg. I then decided to try 89 for a while and get about 23-24 mpg and sometimes even better. No power loss or pinging and a bit cheaper. Was kind of mad for wasting money on the "good" gas for that long. Go mid grade! I have almost 35k on my ride in just about a year so I get alot of data to back up my post. Hope this helps. Electric Superchargers