Higher octanes have a higher self ignition temperature, which has been thoroughly (enough) discussed here.
Modern ECUs have knock detection which 95% or so of the time will detect the onset of pre-ignition (knock) and retard the ignition timing to prevent it. Under most daily driving circumstances, even the spirited onramp jaunt, most people won't be able to tell the difference. If you do notice the difference or race your vehicle on a regular basis, then feel free to put 91 or better in your tank.
Its a personal choice based on your circumstances, experience, and feelings on the matter. Either way, your engine will be fine.
P.S. we all know the real fun is in the corners anyway, so why worry about the engine
