I have a 99 Trooper, my manual says 87 minimum and that's what it gets. We're at about $2.85 a gal. here in NJ (for 87). As was just mentioned, higher octane burns slower and is less explosive. This is why it is better for high compression cars that run 10:1 like the trans am i had, even 89 made it ping. withouth high octane it is more prone to detonate. however, my trooper has a 9:1 compression so 87 actually matches the compression ratio better.

The contradiction is that higher octane usually still feels like the car has more power, maybe because they have more ethanol which releases more oxygen.

Point is, run 87 unless it pings, (manual says a little pinging is fine!). I'm sure your mileage will vary much more with driving habits than the little it MIGHT vary with different octanes.

Just my opinion.