It would be closer than some of us would like to admit, but equally driven cars would have the Mustang GT come out ahead every time.
There is absolutely no traction advantage for the GTP that I know of, and what does handling have anything to do with a straight-line run?
The GTP is about 200 pounds heavier than the Mustang GT...
Also, HP numbers are misleading when comparing N/A to Blower-induced stats.
It's ALL in the power curve, (which by the way makes the LS-1 engine so darn hard to catch..

) Generally, 200hp from an N/A motor will give a much broader and flatter power curve, giving you good hp and torque numbers through much of the tach.... while a blown motor usually has to go high in the tach to start getting some really good numbers out of it. Trying to do this on the Grand Prix's displacement limited 3.8L V6 makes this shortfall even worse.
Even if the hp ratings were the same (which they are not), in general you would have more power more of the time than the GTP.
Heck, by the time the GTP's in it's power band, you've won the race...
Sorry Tim, But the salesman will say anything to sell a car...
Have you test driven a 99 or later Mustang GT? Get on the throttle, and the seat of your pants will tell you the difference by 3500-4000 RPM....
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"The Yellowjacket"
381.8 rwhp 377.6 rwtq
"Never underestimate the power of stupid people in large groups."