High octane gas burns slower and cooler. Dip a finger in 87 octane and blow on it. Its gone in a few seconds.
It burns the same way. Fast and furious. It takes less heat to ignite it.
Sometimes just a hot spark plug tip and a little compression will set it off before it time. Spark Knock.
The compression ratio on the B is low enough to burn 87 ok. But it is borderline. Some bikes with a few tenths higher compression may knock on 85-87.
If you have the knock, higher octane will cure it.
I never run less than 89 in anything. They say you can run 85-87 cause the ECU can hear it and adjust the timing.
To me that means there will be knock on the lower octane. We'll just let the computer handle it.
Nothing wrong with that I guess. Its been that way for MILLIONS of miles on Goldwings, and no problems to speak of.
I believe its just easier on the engine to run a better grade of gas.
We all look for the best oil, why not gas.
Its all a matter of opinion. And this is mine.