Thanks for the input. Maybe I will add k&n and start from there.

To be honest, no I don't feel much difference. I'm sure it's added the claimed 10-15hp in the upper range, but it's hard to feel that on a 332hp car. I think in order to feel a gain you will need to combo the exhaust with an intake and some HFC's. It's a combination of parts that will get you the most gains. :-) it does sound a bit better though.

do you notice much performance difference with the nismo exhaust?