Err...well....you're closer than the OTHERS on here.
In truth, higher octane is used on engines that have a higher compression ratio. The higher the compression, the higher the octane needed to get best performance. Note: this does NOT mean that higher powered engines take higher octane!! My fiancee has a Suzu SV 1000....he takes regular because his engine has only an 11.1/1 compression ratio. Ours, however, has a 12.2/1 ratio....(we drive the de-tuned R6 engine that has a 12.4/1).
We take premium because our engines create more pressure on the cylinder walls, and can utilize all the gas that's in there. If you do this with regular gas in ours, you're forcing a ton of pressure onto a piston to pressurize something that's (essentially) already burned....you got that extra pressure from the OTHER pistons pushing too hard on the crap gas in the other chambers, and now you might as well have put in 75, because that's all the power you're really delivering to your wheels. We're already only putting about 88 ponies on the ground...and the power band already doesn't kick in until about 7500 rpm....why make it WORSE?
When you bought the bike, it had two stickers on the tank. The one on top tells you to wear protective gear, daggit! The one *below* tells you to use premium, if you paid any attention before rippin them both off. (I barely did.)
I have a VW new beetle. It's miserable, but if I put supreme in it, I get no milage...it doesn't have the compression required to USE all the gas that's in there....but regular gives me GREAT milage. My firebird, on the other hand, uses premium when in good tune, and will do 70 mph at 1500 for half a billion miles. Put in regular? and I leapfrog from gas station to gas station.
So. Yeah. Premium. Unless you're in oz, in which case, you can use mid-grade.