If you had access to a dyno with an exhaust gas anylizer and started making back to back runs,while increasing the octane number every run,[and not changing anything else] you would soon get to the point where horsepower loss would start occuring. You would also notice that your air fuel ratio would constantly begin to get richer and richer as the octane number got higher by using the exhaust gas anylizer. Our busas are designed to run efficiently on a certain octane fuel,[I guess 87 to aprox.92 or 93 octane]which would be what is available at all the pumps everywhere. Once you get past that efficient octane number the mixture just gets richer and richer, and that is where the performance loss comes from. Race gas certainly wont hurt the engine but numbers in the 100's would certainly hurt performance. You could lose performance even from 93 octane depending on the state of tune your bike is in. If you have an airbox mod and your bike runs a little lean, but you really dont notice it because it runs stronger than stock anyway,you would feel performance gains by going to a higher octane fuel,because the air /fuel ratio would get a little closer to where it needs to be. But if you kept going up in octane[say to 115 octane Klotz racing fuel for instance]you would go past that ideal ratio again and start running rich.[losing horspower] Ask any good tuner on these boards and they will tell you one of the easiest ways to lose power is to be too rich on your fuel/air. In states where there is a lot of high elevation,[Wyoming,Montana]most of the gas available is 85,87 and 91 octane. In states with elevations nearer to sea level most of the pumps are 87,91,92 or93 octane. You can see why Suzuki chose 87, because you can usually always get that fuel rating. Like JC said,[in 3 sentences]87 is good enough GENERALLY speaking. If you dont have the compression to squeeze higher octane fuels tighter,and the timing to light it off,it wont burn properly. Or wont burn completly may be a better way of putting it. The higher the octane number, the more resistance to detonation there is.[the harder it is to ignite] Sorry for the long post,JC said it in 3 or 4 sentences,but I thought it might shed some light on the subject.