You can certainly use the stock motor to run the Titan, it will just provide a lot of Torque. This isn't an issue at all and will certainly push any filament you feed it. One of the advantages of using a geared extruder is you can use a motor with less weight.
This means your carriage theoretically, can run at a greater speed.
Edit: I think Colin only has one type of motor, so if you purchase it with the Titan you will get the typical motor. Also, take a look at this review:
https://www.youtube.com/watch?v=tiAQ9slUZ58&t=3s