Good choice with the roadster! Enjoy driving it with the top down, now that the summer is on it's way.
I had to replace the OEM system on my roadster a few months ago. Opted for the Milltek, great quality exhaust with a good, muted sound around town, but then sounds great when you can use full throttle on open roads and hear that V6!
As Arran says, Milltek or Cobra, depends on what you require from your Zed.
Whatever your choice, I'm sure you'll enjoy driving it with the top down.
No better sound!