N/a they're not really worth it. If you got a blower or some type of force induction they can be just as good as L/T's if used with the right combo of X pipe and catback.
The sure make your dumped flows sound a hell of a lot better. On the top end you notice a preaty good difference. I didn't do a dyno but there is for sure some increse. I say get um
i went with JBA's because there are strick smog laws where i live. i gained .2 and 1.5mph with them on my otherwise stock exhaust. but i am blown. it made the exhaust slightly deeper and slightly louder.
they say you may get about 9rwhp on N/A applications, but you will certainly see gains if you supercharge the car. if you can though, get long tube headers.