To be honest, a whole cat-back system won't give you much, if any, performance increase. (If that's what you are looking for)
If you are looking for sound only, the muffler only option is a good one.
For a noticable performance increase in your exhaust, an X/H pipe is the way to go.
Of course, If you spring for an X/H-pipe and mufflers, you might as well get the entire cat-back with the mandrel bent pipes. (What's another 100-150 dollars?
If your curious about the sound, I've got a Bassani X pipe with Dyno-max cat backs....
You can check the sound out by clicking on the sig below..
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1998 Mustang GT
14.18@100.56
"Traction Impaired" or "Nitto Needy"