Are the stock cats free flowing enough, to get just a muffler?

take the cats off, what I plan on doing

Taking the cats off are illegel and will ensure that your X doesn't pass expection. How much power are you looking for?

400 horsepower

400HP?

So the VG33 is moving out eh...whats taking its place?

Meat head

heres what you do

1) Buy 1 magnaflow hi flow cat
2) Buy a aftermarket muffer (if u don't already have one
3) Go to the nearest Midas and tell them to repipe from after the 02 sensors to a turn down (dump pipe) after the muffer with 2.5 pipe. $90 for welds and pipe.

So now you have :

Headers--o2sensors--y pipe--1 hiflow cat--muffer
--Turn down

Any recommendations as to what cat. to get?

sweet. great idea!