One question for zephyr. I saw the pictures of the exhaust on the link you posted:
This is interesting, I thought they used an electrical valve, instead they used a vacuum actuated valve. So did they fit their own control system connected to the intake, running the pneumatic pipes all the way to the front of the car?
This is more expensive but also better for reliability, as there's no electrical parts close the the exhaust, just a mechanical system.
By more expensive I mean around $ 1000+ between the box with the solenoid and the remote receiver, the remote and the pneumatic valve.
The headers are a let down, and I think the power increase will be very limited...actually I think there will be a power loss:
The primaries are shorter than stock, as well as the secondary.
Plus if this is the cat:
It's very small and placed close to the engine...
Buf if I understood correctly you didn't fit the headers, just the overpiper-back system, right?
The front and centre pipe are direct pipes, right?
This means that if in the future you'll replace the headers with catless ones, you will get a very nasty metallic buzz.