What do u like really is what it comes down to. Not much difference performance wise from 4-5in. Do u like the big exhaust look? 5in might be a little louder. Maybe. I went with 5in just because i wanted it. I would straight pipe it if u like hearing the turbo. Take cat, muffler bye bye. And run a diamond eye down pipe. That was my setup before i put twins on. Sounded nice.