As I have read on this site, you will NEVER outflow the factory exhaust. For us, changing the exhaust system are for these reasons:
1) Cat converter is shot and you get more for the money by going to a full exhaust upgrade as opposed to just "cut and paste". And ideally, this is the way to go, but sometimes money just doesn't allow that.
2) You want to be heard.
That being said, performance wise you should not see any difference between a good factory muffler (or OEM replacement) vs. a custom muffler. Where the gains come from (and it isn't so much a gain as it is a restoration of lost power) are when we change the cat converters. A resonator is really nothing more than a glasspack in most cases (though they can *also* be constructed similar to a genuine muffler) and again does nothing for performance but rather "tunes" the note of the exhaust.
My suggestion? If money allows, make it to where the new exhaust is sectional. That way, you can easilly bolt in the resonator (or straight pipe when the res is bypassed) to suit the situation. For long hauls, go with the rez. For around the town or street/strip, take the rez out. Simple!
Welcome, downwardly mobile yuppies, to the dawn of the Age of Nefarious.
1993 SSEi - FrankenJinx - dead and gone.
1994 SSE (136K strong) - 180* t-stat,HD alternator, most unequipped SSE on the club, XM radio, Kenwood CD/MP3.
2006 Chevy Malibu Maxx LTZ - Custom 2.25" manifold-back exhaust w/FM-80. Probably the only Maxx with this system.