If you are looking for horsepower gains you will gain little from the high flow cat, either one. They do sound better, even the straight downpipe with no cat has only small gains, I have had and dyno'd them. The factory exhaust is a very good one just too quiet, it makes plenty of power with a good tune, factory cat is also not that restrictive, I am actually putting mine back on to replace my downpipe. Do whatever changes you like have the car retuned. The intercooler makes a huge difference, it means your car won't heatsoak and will continue to perform after it gets hot (like when you drive it). On the dyno one run and the factory IC was heatsoaked. You guys can bench race all you want dyno's are a tuning TOOL, they don't mean squat.
Solo Mach and No Cat custom A/R cone
Dejon Intercooler, Intake Elbow, BOV spring
Wester's Garage tune
RMR Style Bar.
SSR Type C wheels, Nitto 555's
DDM Works PINK Breastplate, PRO Beam
GXP Z0K rear sway bar with urethane bushings
Custom Jonymac glass wind screen, one of a kind.
Eclipse AVN726e; ZED Audio Leviathan, Image Dynamics tweeters, CTS door subs, active crossover tri-amped. Audio Control 6 channel 30 band parametric EQ.
JL Audio 10" sub