It says on that pretty spec sheet that it's running a Powerplay-tuned ECU.
Best bet is to call Alistair and ask him what fuel he tuned it to... Hopefully he tuned it on 95 for safety, but if he tuned it to 98, just turn the boost down a bit like you planned, and she should be fine. If you're REALLY worried, get the timing retarded a bit.
Forget those octane boosters. They don't work and just foul your plugs.
edit: Damn you Dundan, stop copying me