With respect, I do still disagree. I am running a catless dp/rp into the stock CBE and a CAI on intake side (see sig below).
I know vendors want to sell product. I respect that. But I have tested my car with these mods (prior to the Hypertech tune) by making 60-100 mph runs with an accelerometer. I did the testing with the racepipe connected to the CBE and with the CBE disconnected and just hanging below the racepipe. The times were identical. The stock CBE flows that well.
On turbocharged applications the absolute best power should be with no exhaust system at all -- a dump straight out of the exhaust manifold through the turbo and wastegate. So, with a 3 inch catless downpipe and race pipe, that's as close to a dump as you are going to get. If the acceleration times are as good connected to the stock CBE as dumping from the race pipe, which they were, I can't justify the expense of a different CBE.
If I thought any CBE would produce measurable power gains (at the track or by accelerometer or stopwatch) I'd be all over it. It did not happen for me.
OP, please search. There are lots of threads here and on other boards (like the one with "speed" in its name), where this topic has been discussed over and over again. If you want a change in sound, by all means, change the CBE. If you are looking for a usable power gain, I suggest you consider any one of many other mods that will actually bump up the power. Just one opinion . . .