Coming for a Mustang to the F I know that you can never take a GT too lightly. There are guys running 375-400 rwhp n/a and well over 400 rwhp FI. All for thousands less than even the deeply discounted Fs cost. Granted, I would never trade my F for a Mustang no matter how fast it might be.. . . . and a Mustang GT (V8) costs about half of what an IS F does.