It depends...
depends on your boost, and your tires. what do you plan on turning your boost up to, what kind of tires are you running, and what kind of boost can you build at the line? Another thing, I race mustangs daily (when it was nice weather out) and I'd say 60% of them NEVER disclose their full modifications. When racing the latest generation mustangs (not the fastback throwbacks) automatically assume cold air intake, header back exhaust, and chip/ecm. right off the bat, and go from there. With just those mods, properly tuned 2000-2004 GT's are kinda quick. If he knows what he's doin on that stick, don't under estimate him. Their throttle response and low end torque can be quite impressive.
But, with your combo, a TRUE cold air intake (which if its the big mouth i think you have, youre good to go) good exhaust, the boost turned up, some good MT tires, and a decent launch, theres no reason you shouldnt take him, providing you havent been running all nite, and have some heat soak goin on. I'd bet on the GN on that one.