I've tried running 93 Octane and haven't seen any measurable benefit. I track fuel economy and that definitely didn't improve when I used 93 octane (this surprised me). Subjectively the performance seemed the same. I suppose if I did actual HP / 0-60 measurements there might be a difference but since I can't tell the difference in everyday usage I cannot justify paying 20% to 30% more for premium.
Around here some (not all) Circle K's and Kangaroo Station actually sell brand name Top Tier Fuel. I regularly stop at a Circle K that sell Shell Gasoline and occasionally stop at a Kanagaroo that sells BP gasoline. I also buy a lot of gas at Costco which is Top Tier gasoline.
One thing to consider if you start having fuel problems when the fuel tank is half full is the performance of the right side fuel transfer unit. Mustangs have a double / split bottom fuel tank. Except when the tank is mostly full, fuel has to be transferred from the right side to the left side (where the main pump is located) to completely empty the tank. If the fuel transfer unit isn't performing properly, then it is possible you are actually running low on fuel if the left side of the tank even though the gauge may indicate a half full tank.
Ed
