The higher the octane the less volatile the gasoline is. Higher # doesn't necessarily mean greater performance.
I would say use the lowest octane rating that doesn't cause pinging (which is pre-detonation of the fuel). If it pings go up to the next octane level fuel.

If pinging isn't noticed an increase in octane will do nothing for you except burn a hole in your wallet. The only time I've experienced improved performance is in a V-8 boat engine. The higher octane gave me ~400 more rpm at full throttle. This translated into 3 mph added to the top end. Probobly helping the fuel burn more completely at the higher sustained rpm. Its surprising that most people think high octane = hotter burning. I see alot of people putting it in cars that don't require it.

If done right, makes a nice looking display item.

Specs and pic... Shown with decals, but could be painted or detailed anyway you like...

http://www.tamiya.com/dtst/58182.htm