I already searched

Ok, I know exhausts have been covered numerous times, I searched and read several, but here we go...
When we bought we went with the non-supercharged as we didn't want all the upgrades that came with it. Wife agreed(at the time anyway..) that I could spend the difference between the two( some $3400) to increase the HP in ours. FIPK is on, now to the exhaust. I read alot about the 'y' where the two meet, but ours is not like the ones described, we have a true 'y', not a 'T'. Also hear about unbolting behind the cat, we have 2 downstream cats (4 total) and no bolted fittings, all mandrel bent nice curves... no real complaints other than the huge muffler, I'd like to get rid of it just for the weight savings alone. Can any one convince me why I need an entire cat-back system rather than just replacing the muffler with a high-flow design? Cosmetics mean nothing to me, neither does brand name or warranty promises, just performance. Price is not a prime consideration, but the high-flow muffler will set me back less than $100( hell at that price I may do that just while making up my mind on anything else...) while all the other systems which don't seem to have any advantages cost over twice that. Any info would be appreciated, esp. from anyone with exp. with a 2003. Thanks.
MV

Why buy a whole exhaust system when the one you have is brand new? If you want to lose the muffler or trash can whatever that huge thing is Nissan put under there, you can get a Borla muffler off Ebay for @$85. It sounds good and you'll notice a difference in power without the restrictive monster muffler.

With a certain cat back systems you get slightly larget pipes than stock, plus many come in stanless or aluminum so they wont rust as quickly.

Take a good look at your Y pipe. I know that on mine one of the pipes going into the other is smaller. In fact its the smallest diameter on the exhaust as far as I can tell. I was thinking of having a friend fab me a new Y-pipe that isn't so restrictive.

But if everything looks sound to you just get the muffler.

The primary reason for a Cat-Back exhaust system is to make it easy for the DIY'er to change out the exhaust system without the need for welding.

In reality, the X's factory exhaust is not poor, but not biased for high performance. The only reason to change to the Cat-back system on a brand-new vehicle would be to get rid of the pinching of the tube that is evident in the turns on the OEM exhaust system. The aftermarket systems use a different tubing bender during manufacture to help keep the bends consistent in size with the straight pipes (no pinching)

If you change the muffler alone you *may* notice some horsepower increase, but nothing drastic. As well, you would have the same results with the Cat-back system. The Factory muffler is engineered to be: (1) quiet, (2) flow well...so a high performance muffler will help the power, though result in more noise.

I installed a muffler only on my truck...initially a straight through type (too loud), and settled on a turbo-style muffler. The sound is not too loud, and has a grumble at idle. However, it is not the most efficient, as you can still hear the exhaust "woosh" when you are under a load with higher RPM's...indicating that the system is still restricting the flow engough that you cannot "hear" the exhaust pulses.