I had a cat back without a resonator, it sounded like a herd of killer bees... Way to loud. Way to obnoxious!!!! I ended up putting a 16 inch glass pack in for a resonator, now it sounds KILLER!

 

Don't do it, keep the stock resonator on or go for a shorter one if you want louder in sound, but it won't help anything on the performance.

 

are you saying a test pipe won't improve performance at all???

I have one, but I haven't installed it yet.
also...don't install a test pipe if you live in an emissions tested state.haha.

 

Getting rid of just the resonator will only affect the sound. It won't help much with power.

Getting rid of the cat can add power depending on the condition of the cat. If it's old it's probably gunked up with years worth of smog then it's definitely killing power. If it's brand new then it's not much of a power drain. I'm more inclined to replace an old gunked up cat with a high flow unit rather than a test pipe; mainly because running no cat makes the car smell horrible. Plus all those unburnt hydrocarbons are bad for the environment even if you don't have emissions testing. I don't want every car to be a ULEV but a certain amount of responsibility is in order.