A lot of time has passed between 2006 and now. There's no telling what if anything, has been done to your car. The easiest way to tell what works best is to just try it. Fill up, test your gas mileage and compare it. The more times you do this, the more accurate your results will be.
Personally, I'd skip the 87 octane all together and do my testing on 89+ with base timing bumped up a degree or two. Since the octane rating has [zero] to do with energy produced, it is useless to run a higher octane than what is required to resist fuel detonation prior to spark. Running 93 octane in a 2006 that is N/A would be a complete waste.
