9.5 to 1 does sound a little high for 89 octane, but just this last week I was listening to a talk show discussing an article about higher octane fuels. It said using higher octane on cars that did not call for it was a complete waste and that in fact most cars calling for the higher octane would run just fine on the 89 octane.
The 89 octane is worth a try. That car should have a knock sensor and it will back off the timing so the engine should not knock which could cause some damage. Listen for detonation as 78 monte said. Don't fill it all the way up all the way the first time and have a can of octane boost in hand, just in case. The worst that should happen is you will notice a drop off in performance & fuel mileage.
Also how hard you drive it will have a big effect. Let us know how it turns out