IMHO i would stay with the stock exhaust system with you living in California, which is horrible for enforcing emissions and noise regulations. I would have a Quicktyme Electronic Cutout installed and have the car tuned to run in the open position. That way you are emissions legal under testing and as quiet as a church mouse while driving in the car for any amount of time. This way you have the best of both worlds.

 

I've been running with a dp, testpipe, and stock "cat back" for the past several years here in Cali without a problem. Just put the stock cat on for the test, every two years. I'm also considering a quite cat back system. Have you decided which one your going to go with?