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.