Kakimoto Full Mega N1. Had one on my car. Sounded absolutely nuts!
2.8, GT-RS's, E85 and 30 psi netted 414 rwkw with the mega N1.
2.8, -5's, E85 and 24 psi made 424 rwkw with a twin 3 inch.
smaller turbos, less boost, made more power.
Here is a back to back.
So, you can have the mad exhaust in a box that comes with a few stickers so you can add it to your shopping list OR you can put something on that performs. To get more air in you first have to get the exhaust out.
Edit - Just realised that's not the overlay of the 30 PSI run with the RS's, only the 25 psi. Either way, an extra 5 psi made 13 KW. What a nugget :p.