Actually, the best bang-for-the buck on C5 exhausts IS the Z06 system. Many Z06ers, wanting to be loud, take off the Z06's titanium system and put on an aftermarket unit. What they don't understand is 1) the Z06 exhaust is pretty good up to the 450-475hp level and 2) because it's ti from the rear connections back, its very light. Taking weight off the car has nearly the same result as increasing power so you gain a little power with the Z06 exhaust and you gain a tiny bit more performance by taking 20 or so pounds out of the car.
Better yet, is you can buy C5Z take-off exhausts pretty cheap.
As for Bassani, I have no personal experience with Bassani products for the C5 per se, but in the process of some research I did for an aftermarket exhaust "buyer's guide" I did several years ago, I looked at Bassani's stuff and I think they make a good quality product which is well-engineered.