u/BloodOk8543

I bought a blown evo off someone off marketplace and I've been slowly returning it to stock

The thing that's been troubling me is that I need a downpipe. I am trying to choose between stock and a 3inch downpipe. The rest of my exhaust is 3 inch I am puzzled weather having a stock downpipe with 3 inch exhaust will effect back pressure.

It is to note that this car has the supporting mods to comfortably make 320 horsepower apart from injectors, but this power figure is out of my budget right now

Can someone give me some guidance to this conundrum.