Get the ecu mapped with an EcuTek map that was designed for 91 octane, but will adapt (for more power) if you run higher octane. There are 2 ways to tune a car. One way is at the limit of whatever octane level you have and another way is to tune it just like Subaru did.... i.e. for 91 with the ability to advance itself if higher octane gas was available. There are EcuTek tuners/resellers in the States that use this method of tuning... but the majority put the blinders on, tune to one octane level, and leave it at that.