the Z06 exhaust will make some minor improvement. But it won't be a day/night difference. Most of the exhaust note change will be heard by those outside the car.
I went with the Z06 cat backs mainly to save weight and gain the better lookign tips. Outside my 2002 Coupe, I do notice a deeper idle, and the WOT is stronger. But don't make a mistake by thinking they'll be as loud, or louder as afetrmarket catbacks.
You can get some pretty loud aftermarket catbacks, but if you are looking for a touch louder than the stockers the Z06 Tis are good. They still have a quiet side to them at idle, but can sound pretty good at WOT.
Try some sound clips of the C5s with the ZO6 exhaust.