Your engine will tell you if the octane is too low. If you use higher octane than it needs, you won't hear a thing, but you'll spend more than you need to. Here are my experiences with four Honda 6 cylinder engines:
My 1998 Valkyrie Tourer runs fine on any fuel I feed it, even the 85 octane junk they label as regular in high altitude regions, like where I live. I usually use the 87 octane ethanol free they sell at the local Murphy Express because this bike doesn't get ridden much, and I've had problems with ethanol absorbing water when it sits around for a while.
My 1999 Valkyrie Interstate will knock badly in very hot weather if I run anything less than 91 octane premium. Most of the time it runs fine on 87, so I usually run the ethanol free stuff in this one too. The need for higher octane could be because Honda installed an ignition module on the Interstates with a more aggressive advance curve, to compensate for the extra weight.
I owned a 2013 F6B that would occasionally knock on 87 octane fuel. This is a more advanced engine than the old Valkries with 6 carbs, with a knock sensor and computer that retards the timing when knock is detected. You can actually hear this adjustment take place. I remember one very hot day when accelerating hard it knocked for a fraction of a second, then stopped, then knocked again. It went through this cycle a few times in just a second or two. I assume the engine management computer was ratcheting back the timing in increments to compensate for fuel it didn't like. After that I started using premium whenever I rode in 95+ heat. It was very easy to hear this engine knocking because of the nearly silent exhaust note on the 2013 models.
My current 2016 F6B runs fine on 87 octane fuel in any weather. I've never heard it knock at all. I have no idea why my two F6Bs had such a different tolerance for fuel. The engines are supposed to be identical, except for that droning exhaust note on the later versions. I'll add that my 2016 doesn't feel quite as powerful as my 2013.
Higher octane fuel will only prevent detonation; it won't increase performance. In fact, premium fuel actually contains slightly less energy than regular.
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