On the 05+ Mustangs with Cold Air Kits, at least the ones I've seen tested.. They do not gain an ounce of power without a tune. The Cold Air Kits advertised without having to have a tune, we haven't seen a gain.... unless we a put a tune in the car.
Moral of the story, if your going to do a cold air kit... Find a competent tuner who will get you nice safe Air Fuels and Timing + more power and torque