Read your owner's manual. Use it as a base for what works for you, your bike and your riding style. There are so many factors that go into deciding what octane works best for your bike. Compression ratio, plug types, carbeuration and ignition types, mileage, etc.
I just bought an '04 Kawasaki 500 LTD and I only run 92/93 octane in it. Could I run a lower grade? Probably. It is a twin carb design, but the engine is a 10.2:1 compression ratio that was borrowed from the Ninja bike. I believe the higher octane will help keep this bike performing longer.
I have a buddy who bought an '02 Kawasaki 800 Custom (1400 miles) and it doesn't run very well on premium - he was getting a back fire type condition. He had to back off to medium grade to get it to run without hiccup. This engine is 9.5:1 compression, but it runs like a champ.
The same guy has a pontiac Gran Prix with 340k and still rolling. Always used premium gas and routine maintenance.
I have a well-maintained Jeep - 55k miles - that won't run worth a crap on anything less than premium.
Bottom line, run whatever you can run that makes the bike perform prpoerly. Don't lose any sleep if your bike performs well on lower octane.
Read your owner's manual.