Horsepower = (torque X RPM) / 5252
What that means is that torque determines a car's horsepower at a certain RPM. This means that at 2000 RPM, a diesel CX-5 which can put out 310 lb-ft of torque, is making around 118 horsepower. A petrol CX-5 makes peak torque at what, around 3200 RPM? At 3200 RPM, with 185 lb-ft of torque, a NA CX-5 is making around 112 horsepower. Even if the petrol CX-5 were making 185 lb-ft of torque at 2000 RPM, it would only be putting out 70 horsepower. This is why the diesel CX-5 will feel a lot stronger in everyday driving, because it generates more horsepower at the RPM ranges that we normally drive on.
Generally speaking, not taking into account gearing and weight, high horsepower is what makes a car fast. So a 187 horsepower CX-5, will be faster than a 175 horsepower CX-5, even if that 175 hp CX-5 makes 310 lb-ft of torque at the lower RPM range.