I thought your CATs were glowing red for when I saw your Flickr feed. Doh
I mostly agree with you, if I had my time again I would probably do: headers, 2x 200 cell cats (optional/ only if your car is above 100k kms) and delete the third cat. Everything from that resonator back I would leave stock as a rock.
But like you I went balls to the wall with the initial set up with a complete X-force cat back. It was ridiculously loud because the x-force resonator in the centre pipe while huge is still straight through.
Is E85 a thing in New Zealand? If so, try getting an E85 tune. It makes normal driving RPMs so much more bearable (except for cold starts when it will run rich and very loud).
Finally, compared to exhaust mods, how much does the intake add according to the butt dyno?
Edit: I didn't want to make myself sound like a fool cause I didn't know what you were talking about with inserts. Are they these things? If so great minds think alike because I use the same things too (but have gotten rid of them now because E85 does the same job).