Hypothetically. I I removed the CAT, and left the muffler, with just a staright pipe going back. Along with an O2 simulator for the rear O2 sensor. Would I gain more HP, than I lost in Torque due to backpressure?

Your not going to gain any power since you arent modified. It may seem that you got a lil more power but thats about it.

You will gain about 10 hp and about 10 ft-lbs of torque. You will feel it in your pants and hear it with your ears.

Actually you would lose power and torque. Plus you have an o2 sensor before and after your cat, which would really mess up readings causing your car to run pretty darn ugly. Keep the cat, you may gain .000001hp but kill 5000 nice smelling flowers....plus its illegal.

Installing the O2 spoof will take care of keeping the SES light from coming on. Removing the Cat will not affect how your primary O2 sensor reads.
It is a common misbelief that removing the Cat will decrease power and torque. Of course the regulatory agencies and all the public service centers will tell you that to deter you from removing it......and the "Air Care" laws make it illegal in some cities.
...But if you are lucky enough to live in an unregulated area, like I do, try it. I've done it to a few cars and there was always a noticeable improvement.
Not including the actual exhaust headers, the pressure drop across your Catalytic converter is equal to the rest of the exhaust system including resonator, mufflers and pipes.
Driving at speeds above the posted speed limit is illegal too.

Bullet, you have to remember that he'* NA.....he needs the backpressure more than you and I do. We've already had an SE try this, and he lost so much low end, he was pissed at himself for not listening. He has a Cat again. Just a high-flow unit now.

In any case, removing the cat is something I dont really like. High flow is the way to go. You keep the backpressure needed for NA Bonnevilles and you maintain your environmental responsibility.

Sounds better with a proper exhaust set up too

Ok, well then. Hi-flow it is. Its fuuny though, I have a friend with a 96 Nissan Maxima, who removed his cat as well, he seemed to gain some power. On other hand, I have heard that Nissans are very restrictive on their exhaust and intake, so that might be the case.

We're pretty open right from the factory. And the nissan is all about high revs. We're built for low end.

Okay, my turn! The main reason I wouldn't run without the cat, aside from legal/environmental and potential power loss, is the smell. Cars that were made to run with cat'* stink to high heaven without one. Ever get stuck behing someone whose car smells like rotten eggs? Guess why....