From a 10mph roll, I say the GT will walk it for a little while, but the Evo will start catching up.
All depends on how long they go for.
I have driven both, and the Evo has some masive Turbo Lag, and their first gear is real tall, so they would/should start in either 1st gear at high RPM, or 2nd gear at low RPM, and that will kill their time. The GT can wind out first from about 10-30. The Evo WILL track close though, but with an experienced driver in the GT, I gotta go with the Mustang.
Even though the numbers don't lie, I still say Mustang.
What is the Evo, 270hp, and the GT is 260?
GT = Torque though...
It would be close.