Great theory...

[PiCéd]

Interesting thing, a circuit with only a cap and a DC motor, don't care about the quantity of farads of the cap when you turn the motor with your hand or your finger it is always as easy to turn than if you where turning the motor with no load.

[PiCéd]

To the condition that the cap is in serie.

[dieter]

What happens when you add a load in series, eg. a LED ?

[PiCéd]

Mh, the question is more:
What happens when you reduce the totale resistance of the circuit (resistance of the circuit of the motor include)?
Uind=w*N*S*B sin w
w=2*Pi*F
If the number of turns of a DC motor is the same, it is the same inductive voltage.
I=V/Rtot
Rtot=totale resistance of the circuit
P=I²*Rtot=V*I
Uind=V(?)
The same DC motor  and circuit in a lower temperature, the motor in exactely the same speed with a cap in serie, is the cap will be more charged with the same time than the ambiant temperature?
Vind is the same with the same turns with the same B but if the temperature shut down and the magnet is for exemple a neodym, I think it will be a little more B because of the reversibility of this type of magnet.