I agree on scavenging versus back pressure (I just thought it best to leave that sleeping dog alone). I will not speak to reversion issues either, but the cat does act as a significant "reflection" point, dyno charts show it, top tuners work around it.
On supercharged engines there is a benefit in de-cat, NA engines very little gain.
Header selection makes a big difference in scavenging advantages with a de-cat, I can't speak to the stock headers characteristics with a de-cat. Also agree on second oxygen sensor after Cat, it is there to confirm the presence of a cat, but has no input on the actual lean/rich tuning characteristics.
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