Octane levels are all about preventing pre-ignition due to high pressure and temperature in the cylinder, otherwise known as "ping". The higher the compression of your engine the more octane you need. Higher octane is not a more powerful fuel, in fact the opposite. All other qualities of the fuel being the same, then use the lowest octane that doesn't ping in your engine (or cause the ECU to retard the engine). So it all depends on the compression ratio of your engine.
Of course, all other qualities of the fuels are not the same, and you may use a higher octane racing fuel than you really need just because it is better quality or has higher energy content.
It would be best to call George Dean to get a definitive answer for your specific engine.
http://georgedeanracing.com
Greg