The higher the octane level, the less amount of carbon build up you get. Thats why high performance cars like vettes and mustangs use 91. The injection system clogs less. I put 91 in my 2.2 once or twice a year, just to help clean things up a bit. Theres no noticable difference though.
'05 Base Coupe, Blue, 2.2L, 5 speed manual, Too many mods to list in this signature. I'll just say insanely loud system, fully upgraded suspension (nothing original), Intake, Full Exhaust from the engine back, Rims, Tires, etc... Give me about a month to get back stateside and pics will be posted in the vBGarage.