I also suggest that you increase your budget and go for the FRPP Power Upgrade Pack. Have it installed by the dealer to minimize warranty concerns. You can sell the unused BS K&N filter if you don't buy into their hype and get a little bit of money back as well.
Although I suppose anything is possible, I haven't ever heard of Ford denying warranty work for the use of the Ford Racing ProCal tune. I'm really not worried about that, and I installed mine myself.
One thing I know for sure, is that the ProCal and the GT 500 combo make a dramatic improvement. It's how the car should have come from the factory...but without the BS piece of oiled window screen K&N filter of course...
I'm 41 years old, but I would seriously be mad enough to fight someone if they said I had to go back to the way it was stock! I like it that much!
If you are totally against a tune or spending more money, I choose the GT 500 mufflers.
2011 GT Coupe Premium / MT82 / 3.31 / Brembo
Red Candy Metallic / Charcoal Black / 400A
Comfort / Security / HID Headlamps
FRPP M-FR1-MGTB Power Upgrade Package