If you want to keep the main undercar cat go for the CS, otherwise the CP-E replaces that with a hi-flow cat.
Things to consider:
1 - does the stock cat muffle noise more than a hi-flow? I think yes.
2 - does the stock cat hurt performance more than a hi-flow? I think yes.
3 - does the stock cat clean the exhaust more than a hi-flow? I think yes.
So it all depends on what you're looking for and if you have smog inspections too.
