Jonny,
decisions, decisions...
First, what help, is to define what you're aiming at: (some) sound engineering or a real boost in performance (extra horsepowers at the wheels).
If your goal is to improve the sound probably a backbox and removing/replacing the cats will do.
If you go for the performance improvement you need to include the manifolds as well in your consideration and so the replacement of the full exhaust - with the associated costs....
3 options for a full system:
- Orbisoud, but not sure if they still deliver the full system today, probably only the backbox I believe, according to their website. A full system from Orbisoud is loud, very loud....
- K-Tec /Janspeed, Spike can tell you all ins & outs
- Torque Technique / SG Motorsport as in your previous post
Some members here on the forum have a custom system - I believe from RS fabriaction or Prospeed, I don't remember anymore.
If you go for a full system what you also need to include is a remap of the ECU - including rolling road test.