Peter,
I have a combination of TNT headers, high flow cat, and Borla catback and the car sounds great. I was at a Viper dyno event last summer with some other owners and more than a few who thought the Borla's sounded better than the Corsa's.
I also had some reservations about the twin pipe look of the Borla's, but I have seen owners who cut the center portion out and just have one pipe on the end (this will probably increase the temps of the tips a bit, the double walled construction was meant to keep things cool next to the exits).
The Corsa's also stick out of the rear of the car more than the Borla's, this seems to reduce the amount of soot and dust that gets blown back onto the back of the car. I didn't particularly like that look, but some owners like it.
The best thing is to go and listen to other owners and check out their cars, there are going to be differences between all the combinations. It took me a couple of months before I decided, I was lucky that my tech at Valaya had a lot of racers and street cars to compare with. If you have a chance, listen to a car with TNT's, Borla's, and no cats, it will blow you away.