Gutting the cat is more like a bypass than a pre-muffler. I should think that a gutted cat would be much louder than a pre-muffler, and may not flow as well.

Would a bypass with a stock muffler be too loud for general driving ?
It wouldn't be Header Loud would it ?

The muffler does most of the silencing. The CAT just adds to it.
Most people want more cards in their spokes...
...
Oops, I mean a louder exhaust. ;)

I had a CAT that was gutted and didn't like it...sounded metallic and I think my M&K premuffler improved the low end torque when I replaced it too. Sound is so subjective...but if I were to recommend anything I would say either leave it alone or replace the CAT with a premuffler. Does your car need to pass an emission test? if so leave it alone. And like another poster said, no CAT can create other changes like smell....

Emissions is not an issue.
I guess I would want the oxygen sensor port on the Pre Muffler though.

So another option is to just change the muffler section and leave the heat exchanges so I can maintain the heat and defroster functions.