Brannon,
Octane is a fuels rating of it's "resistance to burn". Anytime you compress gas, it makes heat. The more you compress it, either via high compression pistons or forced induction, the more heat it makes. The reason you run high octane fuel when recommended is that it won't pre-ignite simply under the compression heat...it resists it, and waits for the spark plug to light it off. When you're running too high compression, forcing air, and running too little octane, the fuel won't be able to resist pre-igniting, or detonation, and will light the mixture off prematurely. When a piston is still on it's way up, and it decides to blow, and force it down...boom. That's when stuff breaks. So, Dodge figured that with the factory 9.6:1 comp. ratio or thereabout, that 91 octane should be enough. Running higher octane, 100 or maybe even 93, under "normal" conditions will just make it harder for the engine to burn it off. Fuel economy and performance may suffer. That's why if you have a family car rated for 87...anything more is a total waste, and maybe costing performance. But if you have a high comp. engine, especially with turbo, sc, or nos, usually the higher octane the better.
Tom