I don't have any experience in car tuning, I just got an 05 6spd GT and am planning to replace the cat with a resonated midpipe, I have been doing my research and found quite a few companies producing midpipes, for now I am leaning towards the one made by RP. (I am not planning to do any other modifications to the car except the midpipe and the intake.)

1.Can any one offer some opinions on which resonated midpipe works best?
2.Am I going to have any kind of codes (CEL) running because of the installation of the mid pipe? (some of them say that there is no O2 simulator needed).
My limited knowledge leads me to believe that once the midpipe is installed I will have to reprogram the ecu, in order to get the most out of this modification.
3.Is this necessary, how dramatically will this (re programmed ecu) effect the increase in power?
4.Are are there any videos/ sound bytes of cars with resonated midpipe installed. How dramatic is the increase in loudness.
5.Finally are there any dyno/acceleration results for cars with just the above mentioned modes done.