I'd only ever use 87 octane fuel, because it's all your bike needs.
The octane rating of a fuel doesn't have anything to do with how much energy that fuel has. The octane rating is a measure of how resistant that fuel is to spontaneously detonating under pressure. Vehicles with engines that have higher compression ratios squeeze the fuel/air mixture in the cylinder harder, which makes it more likely to combust on its own, a condition called detonation (or 'knock'). Detonation is bad because it puts huge stresses on your engine. One way to fight this condition is to use a higher octane fuel.
Race cars run engines with ultra-high compression ratios, which require very high octane fuels (above 100 RON), which is why people associate high octane ratings with high power (that, and a lot of marketing by the oil companies). But really, if your engine doesn't require higher octane fuel (and the Versys does not), you're not 'giving it the good stuff', you're just wasting money. That's why you haven't noticed any difference in changing octane ratings.
Last edited by Predictive; 04-28-2008 at 10:57 PM.