Professional Answer to Exhaust Size Question 2.5" vs 3"

I asked
("I am installing a 422 stroker in my Duster. About 520HP with TTI Headers. Will I benefit from a 3" exhaust vs 2.5") to an exhaust manufacturer and got this reply:

"550hp would be the minimum for 3" unless you were building a race car."

I still want the 3" so I will probably go 3" anyway.