how much hp HELP

As far as the HP goes, just wait for one of the local shops to have a dyno day and get one then. I think I only paid $30 for one with A/F ratio last time I went.

You're probably around 199-207rwhp, with your power peaking somewhere around 4000 given that you still have NPI intake, cams and heads. Stock, your 98GT should dyno around 190rwhp, given the 225 flywheel hp rating and 15% drivetrain loss. The mods you have probably added 10-15 hp or so.

Do you currently have the Loudmouth 1 resonators? I agree with you about them sounding too raspy with the O/R midpipe. You have to keep in mind, however, that flowmaster mufflers have an offset inlet and outlet, so you would have to modify your exhaust piping to get them to fit in properly and still keep the tailpipes aligned. I would suggest you try the SLP Powerflo mufflers or even the Loudmouth II resonators. Both will sound much better with your O/R X, and you can swap them in with ease bc your catback is modular (any SLP resonator can be used with it).