Hi I have had the R3T for about 2 months now and I seem to get a better range out of 95 or 98 octane - but not huge.
No real difference on power though.
Triumph NZ says 91 is all you need but the mechanic at my Triumph dealership says highest octance is better - cleaner burning etc. He says that NZ 91 fuel has lots more additives that the 95 or 98 stuff which means that the higher octane stuff is cleaner burning and ultimately better for the engine. I suspect NZ 91 is a much different (and quite possibly inferior) product to the 89 octane in the US. It seems you can get anyone to give you the answer you want.
Probably best to try a tank of each - do similar riding and make your own mind up.