ANy RWHP gains with cat back on vette?

Hi Ive got a A4 2000 corvette with ls6 cam , ls6 intake, blackwing cold air and holowed cats. Ive just had it dyno tuned and got only 319RWHP. I can't put headers on car due to extended warranty.!

Ive herd the stock cat back on vettes flow pretty good and not worth getting. But now after dynoing so low I'm thinking about getting one or a z06 cat back. How much gains do you guys see on cat back Corvettes if any?

Also would putting a cat back on now after a dyno tune screw up the tune?

Any coments would be greatly appreciated.. Thanks!

I work for Pypes Exhaust and we just designed a muffler back and get 10 horsepower.