A Cat-back exhaust bolts up to where the downpipe ends which contains the cat. A Turbo back includes the downpipe and usually contains a high flow cat or no cat. The downpipe bolts to the turbo. The turbo back exhaust will provide more gains than a cat-back due to the restrictive stock downpipe. If you plan on upgrading your turbo however, you might wanna go with a catback for now as downpipes are turbo specific.