OK I am no mechanic but my understand is that running a higher octane will actually hurt performance if your engine is not setup for it.

my basic understanding is that to get above 95 octane you will need to advance your spark (timing), which can be done via reprograming your car and secondly your engine cannot handle the compression it will need for this octane rating. To increase compression you could either modify the head or add a device to increase air compression to it or I am sure there are a couple of other mods for this that are probably not worth the time/effort unless you are actually going to race this thing. If that is the case you would probably just want to gut the car and start with a V8 anyways...

-marc