Due to scarcity of 98 Octane (RON) in New Zealand, beyond major centres, I got my WRX STI tuned for 95.
Tuning has been done by David Wallace (tunetechnic.co.nz). I chose David because I had really good experience with him tuning my ST165 Celica GT4 (when he was with torque performance), as well as he has really good reputation.
Thanks to Subaru open ECU interface the process was very painless. The most difficult part of this tuning process is getting fuel tank empty to ensure it has 100% 95RON.
Basically David uploaded new tune at my place (via OBDII connector), and we went for a drive while David was monitoring the sensor output. After some minor adjustments the final tune was uploaded at the end of the drive.
The whole process took a little bit over an hour.
I am very happy with new tune, as not only I can safely fill up with 95 RON (although it is still better to run on 98 RON as ECU will take advantage of that), but it actually performs better.
Highly recommend doing this for every JDM GRB STI in New Zealand (even if it stock like mine).