Stupid question but how much do you drive it and whats the MPG?
I only put about 5000 miles a year on my GT so I will put that or less on the Shelby. Bought the Shelby about a month ago and have not had a chance to drive it much around home yet, only burned up one tank. It seems to be similar mpg's to my 06 GT that has 3.73's as long as you stay out of the boost. I averaged 24mpg over 1200 interstate miles (80mph w/AC on) when I drove it home. That impressed me considering that the window sticker lists 20mpg highway.
The Shelby is a fun car for sure but so is the 2011 GT, good luck with your decision...