Is high test really necessary?

Jordo!

The engine is tuned from the factory to run on an octane (AKI) of 91 or higher.

I'll spare you the details on octane needs, (which you should do some research on), but the short version is, octane represents the ability of the fuel to avoid knock (explained bellow).

Having said that I'll mention three important issues to keep in mind at the pump.

1. A combustion engine produces torque (and by extension, power) without destroying itself rapidly in the process through a series of carefully TIMED combustion events -- that's what the ignition timing tune controls.

2. Combustion events that are NOT properly timed are what we call commonly call "knock" (auto-ignition or pre-ignition of fuel), and knock can cause severe engine damage in short order.

3. Three factors contribute greatly to the likelihood of engine knock: (1) Increases in heat in the combustion chamber, (2) High levels of compression (either based on design of piston of through forced induction), and (3) increased engine load (primarily by way of corresponding increases in heat and pressure within the cylinder chamber in the production of peak torque).

You live in FL and drive a high revving, high output sports car with fairly high compression pistons.

Does going below the recommended octane sound like a good idea, keeping these three points in mind, the nature of your engine and the environment in which it will operate?

If you think about all that and conclude, "Yes", then best of luck to you...

AKI < 91 is not recommended.

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