Two Sedans with more similarities, such as the body structure, starting price, ground shadow size, height, and maximum occupancy, than differences, like the modifications, market segment, horsepower, and fuel economy. First of all, the 2015 Subaru WRX STI has bigger and thirstier engine; the 2016 Cadillac ATS gets 5.2 more mpg. Among similarities are the body structure, starting price, ground shadow size, height, and maximum occupancy.