Oh snap, I didn't realize that Ford allowed the ECU to respond to premium fuel. My only problem with tuning my old stang to run on premium fuel was that I abused the extra power versus trying to get better fuel economy with it. If I wanted fuel economy, I would have purchased a Civic, CR-Z, or Fit. Also, I don't know if I am buying the new 5.0 not feeling as fast as a WRX. While my 2012 WRX is closer to the performance of my previous 2006 Mustang GT, I found the 2011 GT that I test drove to have way more top end power.
One of the first useful mods that I made to my 2006 GT was to purchase BF Goodrich KDW2 tires. Used, it came with Traction T/As, and they weren't the best of tire. The only downside is if you live in an area with ice and snow or where it stays cold year round because the KDWs start acting weird below 50° Fahrenheit. The good news is that it doesn't take long to warm them up. The other downside is they don't last too long either.
Just remember the golden rules when it comes to modding. If you want to make it go faster, you need to make it stop faster while figuring out how to transfer that extra power to the ground. It's a delicate balancing act that usually is offset by the amount of money in your bank account. Go into it with the mindset of expecting things to break, and hopefully nothing will. I was lead to believe that my 2006 could handle the extra power from the CAI, tune, and sticky tires. It couldn't.