i had the mac( old one) the type that was like the dence charger. fender well type. it was terrible! made the car hesitate a bit in every gear. once the car got going it seemed to be a small pick up over stock. however it had the 90% bend that the d/c also has and i hear that some people have lost power because of that.
i got the steeda one and it looks awsome compaired to the other.
i would say i got a decent gain over stock and a small gain over the mac. cant really tell but the car runs smoother now and has no more hesitation.
i think it was because of the bend in the old pipe, car wasnt breathing right.