Since we're talking about NA Subaru 4 cylinders, which all have a redline within 200 rpm of each other and conservative cams, we can generalize here. Your point is correct when talking about other makes or about highly modified Subaru motors.

Piping size most definitely matters with turbo exhausts. There's really no "too big", although bigger than 3.5" just doesn't really fit under the car, although there is definitely too small.