Higher octane is better; i was referring to Arco's 87 vs Shell's 87 (i.e. same octane at different stations). Before I got tuned, I had switched to to 89 (from 87, which is the basic here in Cali). When I did that helped out my car alot.
Now after having been tuned I'm running 91 all the time (highest out here, with the except of Trick Fuel, @ $8/ gallon