Dual-Mode Performance Exhaust v. Cat-Back Exhaust

Hi All:

I'm getting ready to order a 2008 Convertible with paddle shift automatic and am considering ordering either the Dual-Mode Performance Exhaust option (6hp gain), or the dealer installed Cat-Back Exhaust option. Can anyone give me some info. as to which one is a better option? Which one may give a better sound? Which one may give a larger horsepower gain?

Thanks, Scott