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.