All three, just a catback, just a midpipe??? Do you have an intake? Pulley? Will you be running stock boost or boost jets to get the most out of your ECU upgrade? You do know that with a 96 you started out at 280hp don't you?
If you have a legitimate stage III I believe you should be able to run in the mid 4's and around 13. (I am just guessing that from what I recall reading) Search - this has been covered before.