I have an Audi TT (attached in
this post) that requires a minimum of 91 octane. Seeing how regular is only 83 octane and super is only 87 octane, you can see how I am forced to use premium. Seeing how I only drive the car a few days a month, it doesn't hurt that bad to fill it up. When I first purchased the car I drove it up and down just to drive it and it made a pretty big dent in my wallet to fill it up. But its not too bad.
And yes, the octane does make a difference. If i were to put super in the tank the engine would make a loud clanking noise, like a diesel. and it would occasionally stall out. If I were to put regular in the car, it would just repeatedly stall. I let my brother drive the car once and he filled it up with regular gas and the car didn't make it out of the station's lot. We had to siphon the cheap fuel, put it in my truck and put a quarter of super to help the car burn the bad gas. its a small price to pay.