has anyone tried putting a full (turbo back) 2 1/2 mandrel bent system on their VNT car? does it cause the car to overboost?

what about 2 1/2 mandrel cat-back system?

what about just putting a good free flowing 2 1/2 muffler on an otherwise stck exhaust system....like a walker ultraflow or a magnaflow?

I want to free up the exhaust flow a good deal but not so much as to cause the car to run lean with the stock injectors.