Sorry I can't help you with your question, but I can Welcome you I'll let one of your fellow C5 Brothers/Sisters answer you exhaust question.
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I have the Corsa Indy system on my car and love it. It has no interior resonance, and is only slightly louder than stock at a steady RPM, but is very aggressive under acceleration. The Corsa system does pop & crackle a lot when you let off the throttle, it's sort of a love it or hate it thing. It's less noticeable on Auto's vs. MN6 cars, and the addition of an X-pipe makes a big difference. Corsa also makes a touring system that is a little less agressive at WOT. The first B&B systems seemed to get a lot of complaints about interior resonance, but their new PRT systems claim to solve that. I have heard a lot of good things about the B&B PRTs. Borla and Bassani are also big players in the C5 cat back market. The quality of the Corsas on my car were top notch, and the install was about 1/2 hour - I had a local Chevrolet dealer put them on for $35. It really comes down to what you are looking for, and I would highly recommend listening to the various systems first, and if possible, getting a ride in a car so you can hear the system from inside the car under a variety of conditions.
At the labor day event at Bowling Green, We ask Jim Browning and Paul Carver of Corsa to give my wife a ride in their C5 to listen for interior noise.(It's her car) We now have their Indy's and like them. The people at Corsa were great to us.
I can't say about the others, but do yourself a favor and go for a ride in a car with whatever you think you want to buy.
My fuel mileage may have suffered due to the change in my driving, just love the sound.
I dont know about the resonance, but I have heard that some after market manufactuer's (Borla is the name that pops to mind, but dont quote me on that) are getting ready to introduce a titanium exhaust system for the C5's, very simmilar to what is on the ZO6. For the C4 owners out there, I have heard rummors of a titanium exhaust for C4's also (not sure about the ZR-1's though). From what I have heard the weight savings is about 45 lbs, but you pay out the @#$ for it. No numbers on HP gains though.
I cannot speak for other exhausts, but, I am very satisfied with my Corsa Indy's on my C5. They offer a rich sound at WOT and I have no interior resonance at all. The quality and fit are beautiful and they come with a lifetime warranty... Do get an X-pipe installed for added sound quality and it also reduces popping through the exhaust. It would be my suggestion to listen to as many different exhausts as you can for they are very subjective!