Well, I've only had the car about 6 days, but here are my first (very nontechnical) impressions.
First off, power/torque feels fairly similar. Unmodified, the 1999 mustang was rated at 260 hp @ 5,250 rpm and 300 lbs-ft of torque at 4,000 rpm...never dyno'd that car, but i'm pretty confident...