Performance or not, the engine was designed to take a higher octane fuel...seriously it's $2 - $3 more. If people are so hard up for cash, sell the car and buy a Civic

Also, the points of that it lowers efficiency negates putting in cheaper fuel since you'll have to fill up quicker and eventually, over the long haul, spend more money on fuel. I'm pretty sure the engineers know more about what needs to go in the engine more than 90% of us here do.