The GTR has some power adders, weight reduction, cage, race equipment, but is mostly stock suspension components underneath (disregarding the shocks).

The Mustang has a 550whp race engine. The suspension is completely custom underneath. It's basically a caged Mustang chassis dropped onto a full race suspension and drivetrain. For the most part, the only thing Mustang about that car is the bare chassis itself.

The Mustang was definitely faster in the straights, but lacked the corner entry and exit speeds the GTR had. However, they were very evenly matched. Given both cars having different strengths and weaknesses, it was interesting to see how they battled around the track.