Have a read of a thread I posted last week - I found somewhere that sells 5 star petrol - 102 octane
The higher the octane level the less chance there is of det, meaning you can advance the timing a little for more power
Turbo'd cars will benifit a lot more from a higher octane fuel, but go to high, and you will get cold starting problems as your plugs will coke up as it will burn to cool
PS That 102 octane stuff is a
leaded fuel, and if you have a CAT will be of no use to you. The lead will break the CAT down and its efficiency will suffer