[My87z28]

If you plan to keep the car stock, with stock exhaust then I'd recommend the NPP. Especially if you ever care about driving with the car more mello toned. However, if you plan to modify the exhaust and care less about ridding around with a more mello tone, then I recommend the non-NPP. A full cat-back NPP compatible aftermarket exhaust is going to run you $1200-2000, not including install. However, with non-NPP, any custom exhaust shop can build you the exhaust you want for $400-800 depending on mufflers and materials used. I have non-NPP (because I knew I wanted louder than NPP),I had a complete custom cat-back, 3" stainless pipe, X-pipe, 6" flex pipes, flowmaster 10's, flowmaster 4" double wall tips installed for a total of $700. Now if you are stuck on the looks of the gloss painted exhaust defuser and dual quad set up of the NPP but know you want the car louder, you can order the exhaust defuser from thatgmpartsguy.com and have it painted for around $350-400 total, then buy higher quality dual quad tips for another $150-190. So you can have the look of NPP with the sound you want for $900-1250. By going the NPP route, you already paid $900 for the exhaust option, then you'll pay $1200-2000 for the cat-back, and another $200ish for install. For a total of $2300-3100.