sagebel
Stock? Pfft!
Sounds like a good excuse to buy a turbo back exhaust. Welcome to SDD!
Don't do it. I did and regret it . . a little. Anyways, to answer your question, I used a two inch pipe and a BFH.
Better thing to do is get what is called a test pipe to replace the cat. Comes time to trade it in or emissions you'll be glad you didn't destroy it.