I've changed from 2.5 to 3" on cars around 500hp, and honestly felt no difference. Maybe a dyno will tell different though ?

Also have cars in the 6-700hp range with 3" without any difficulty. It isnt to say larger may not help...but the 3" certainly posed no problems, and these were proper systems with a couple of boxes so they were quiet so as not to flout any noise restrictions when racing ( Subarus )

One car ran 9.5 at the 1/4 with a full quiet 3" system. I think at testing it was in the low-mid 90's db range. Cant remember exactly, but it was quiet. Far quieter than most of the slower cars.

We did change the above car to a 4", and it did affect tuning and boost control, although didnt really affect times. It has run faster since, albeit with other changes too.

I think people get too hung up on thinking they need a huge exhaust or something. If you have the room for it on the car and it meets noise criteria etc...then absolutely bigger can do no harm.

But if the 3" fits better, is quieter, cheaper, whatever and is maybe off the shelf....it's a no brainer to just use one.