When I worked at the Ford Dealership all of the Mustang literature said a stock 03 GT would run the 0-60 in 5.8 seconds. I have actually seen that time in a couple of different spots. But I agree with the others, there are too many factors so that is just an estimate from Ford.
I have the slips. I'm ashamed to admit that my reaction time is usually a tad slower. I wasn't giving an actual time though. I just think that with the torque a Mustang has, it's actually easier to get a consistantly good 0-60 as compared to those high revving sewing machines. 0-60 on a GT is nothing to complain about.