[Al Skierkiewicz]

Chris,
One of the things that has not entered into the discussion yet is...The brush assy contacts more than one commutator segment at a time. Although it is easier to see using a Victor, the current through the motor steps up and down as the brush assy crosses a commutator boundary. At any one point in time, you can have one or two windings in parallel.
Don't forget that at slow speeds, motor losses become the more predominant part of the model. Bearing friction, brush friction, load losses and magnetic field issues all need to be accounted for. It is very difficult to get the motor moving particularly with small duty cycles. As the motor approaches max speed, the back EMF becomes more dominant.