Performance cat or test pipe?
 

I'm just feeling out a possible future project.

I suspect the stock 20 year old cat on my car probably does not flow optimally any more. I'm thinking of replacing it by either buying a high flow performance cat and having it welded in place of the stock cat/resonator, or sourcing a used y-pipe, cutting out the cat, replacing with a straight pipe, and keeping my current y-pipe to swap on for emissions testing.
I've heard having a cat makes these cars run a little rich due to the back pressure keeping the oxygen sensor hotter. Also, how much louder will the stock exhaust sound without the cat and/or the resonator. I would like to open up the sound a little and still keep the stock look. Also would this kill the low end torque on these cars, even if I keep the muffler stock? I also heard that the feeling of less low end torque from less backpressure can be at least partly attributed to the rich running with a cat, since that person claimed that a rich mixture strengthens low end throttle response, and can make it feel stronger, only to lose power up top due to the rich mixture. I'd imagine this theory is even more pronounced if you go from a stuffed up old cat to a test pipe.
Has anyone tried anything like this or knows what works best.
Thanks in advance!

High flow cat, testpipes only show decent gains with turbo cars.

agreed - generally low end losses and minimal if any high end gains on NA cars - as a part of testing many cat-back systems, i've been playing with this a LOT lately