RE: does it REALLY need 89 octane?
its really not worth it; if you have to, dont run the car hard
if you had a forced induction high compression ratio engine i'd tell you no bueno, but I think you probably got a little more leeway on your engine
but I guarantee you if you don't notice a difference in the performance then your not paying close enough attention to your car.
nothing good will come of this.
If I could I'd be putting 92 in my car!