Are you talking about directly driving the wheels from the output on the CIM's? If so, then theoretically the max speed for the wheels at 12V would technically be 5310 RPM; the actual max speed is a statics problem.
The static max speed of the robot occurs when the rotational force of the motors happens to be equal to the frictional rotational force that's impeding the acceleration. The frictional force is experimentally determined, but tends to be rather proportional to the quality of your bearings and such, and the robot weight.
IMHO, though, you should never direct drive the CIMs due to the issue with actually accelerating up to the top speed in the first place. Acceleration is going to be proportional to the applied torque to the wheels: gearboxes are used to amplify this torque so max speed is reached relatively quickly and the amount of current flowing through the motors during acceleration is limited. Acceleration is actually the hardest part on the robots during the match, and because the output torque from the CIM's is relatively low to geared CIM's, they're going to accelerate slowly and probably throw breakers/destroy themselves if you try this for any extended period.
Edit: If you want an in-depth explanation of how the DC Motors and gear trains work, MIT's article explains it in a complicated but complete way.
http://ocw.mit.edu/courses/mechanica...lecture-notes/