I am going to upgrade to a 2.5" exhaust system. But just cat back won't do me any good really. So what size header do I get? Or is just a "performance" pre-cat delete system all you're supposed to do? I am not going to pay $1k for a header and $900 for the exhaust. There are some performance parts worth the expense but exhaust mostly changes the sound as long as you have the size right so I will be getting something MUCH cheaper on it. Any thoughts?