Think of the motor as part of a drive system as the motor alone does not constitute how well a locomotive will pull a train. The motor is an important component, however consider the size and type of flywheels, command control if any, the gearing ratios and ultimately the amount of weight holding the wheels on the track all factor into the tractive effort of our models.
There are several examples of single motor models that outperform a similar double motored locomotive and the same is true the other way around. It all depends on the model.
