From what I've read on here before, the reason stock cats perform better has to do with the performance curve of the supercharger itself. With an exhaust that is too free flowing the SC can't create the pressure it otherwise would. I'm sure valve overlap, etc. also plays a role in this.
YMMV
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'11 370Z Nismo #528 Fast Intentions | Stillen | Motordyne | Uprev | CSF | Zspeed | Z1 Motorsports | AST | Swift | SPC | SPL | Whiteline | Hotchkis | Bride | Schroth | Robispec | Cusco | Nismo | Volk | Forgestar | Hoosier | RJM
'17 Titan Bone Stock
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