Well, the P2K, P2K2, Monster Stock, and CO27 are all different motors. They all have more than enough torque to do the job with plastic tires, but it's the RPM's that are different with each motor. This is how it goes with the max RPM...

[LOWER RPM]<------------>[HIGHER RPM]
P2K-----P2K2-----Monster Stock-----CO27

The P2K2 is possibly the most popular stock motor since it provides a good balance between torque and RPM. I prefer the higher RPM stock motors since I also race stock class.