2.5" exhaust vs 2.25 or even 2"

IMO , you are giving up both horsepower and torque by going to a 2 1/4" system . I have been told by several manufacturers of exhaust headers and systems that 425 engine horsepower is the cutoff point between 21 /2" and 3" systems . If you have a low production/numbers matching car then 2 1/4" is your deal . If you are planning headers I would go 2 1/2" . If you plan on h.p. upgrades I suggest 3". whats't he harm .