A Mustang GT is a powerful muscle car. A Subaru WRX STI is a performance-tuned rally-inspired car. A Subaru Outback is a family SUV.
* Mustang GT vs. Subaru WRX STI: The Mustang GT generally has a significant horsepower advantage and will likely be faster in a straight line. The WRX STI might have an edge in handling on twisty roads due to its all-wheel drive.
* Mustang GT vs. other Subarus: The Mustang GT will almost certainly be faster than any other Subaru model, including the BRZ, Forester, Ascent, etc.
To get a precise answer, you need to specify the exact Subaru model.
