For the record, we thought the cat-back was excessively restrictive on that '08 with (I think) a Dom 3. There is a two-sided new development -

1) We made 424whp on our Dynojet on the stock cat-back
2) That car had an externally dumping EWG

The EWG is going to be dumping all the exhaust that's not needed to make the boost, so it might be flowing a LOT on that 35R...

Siegel