I have an '08 6m, NPP exhaust w/ mild to wild, Z51. I bought the car new, and it has about 10.5k miles on it. I want to put some long tubes on the car, and was wondering which diameter pipes should I use? 1 3/4 or 1 5/8? Will the stock NPP be ok, or should I go with a different cat-back? I would like that nice 60's muscle car rumble:wheelchair:. Any help or opinions would be appreciated. Thanks in advance.