Also, you would be really surprised to find out the variance in octane ratings at the pump. A lot of times a gas station will have the tanker pump low-octane into the premium pumps. The stores can get into big trouble for this, but the "foriegn owned" stores don't really care and they are the worst offenders.
Another issue with octane I didn't see mentioned is the mix of gasoline vs ethanol to get to a specified octane. For example, QT purchases low octane gasoline and adds the maximum amount of ethanol (10%) to get to 87 octane. This benefits in lower costs for gasoline and more subsidy reimbursement with the ethanol. Not all retailers do this, but I know QT did through 2012. Other retailers would purchase 87 octane and then add 10% ethanol and the end user was getting a higher octane than they were paying for. I do not put ethanol in any of my vehicles or equipment.
Because ethanol has an octane rating of 113, adding 10% ethanol to gasoline raises the finished fuel's octane rating by 2 or 3 points, improving the fuel's performance.