For a stock Stang, shortys and mid pipe will give more gain than a tb & maf which most peeps usually go for first. I guess that is most likely cause they are an easier mod to do than exhaust.
Even if you already had an intake, the tb & maf really does not give much gain until you open up the motor for a good bit more air flow and that means better flowing heads.
The biggest rip off for gain got has to be a cat back.
Then again, 95% do that mod for the sound and not for the gain
Grady