Richard, you are absolutely right about lower octane gasoline being more volatile. This is the reason that, under the right (or should I say wrong) circumstances, pre-ignition or detonation will occur. If the engine's compression ratio is too high, the heat caused by that compression will cause the fuel to ignite prior to the properly timed ignition spark.
However, high octane fuel is NOT good for engines designed to run on lower octane gasoline. The reason for this is that the air/fuel mixture is not properly pre-heated by the compression of the cylinder and therefore does not burn efficiently. This leaves carbon deposits on valves, pistons, etc.
The bottom line is this: If the manufacturer says to use a specific octane fuel in that engine ... use it. If/when the engine begins to ping, upgrade to a higher octane fuel. Understand, the likely reason it is now pinging is because of build up on the piston or the combustion chamber thus decreasing the volume of the combustion chamber and thereby raising the compression ratio. Other factors can include timing belts/chains, bad fuel, or an older vehicle that was meant to run on leaded gasoline.
