Think of power and not just current. Power is like the light bulb ahead, it tells you how much work is being done like a light bulb rating tells you how much light it produces.
Wiring in series/parallel wouldn't matter if you could deliver the same power. However, if you have lower volts then parallel makes more sense and if you have extra voltage then series makes more sense. (this is assuming that you're using a PWM controller to control the current and not resistors although the example still works)
The inductance of the coils will rise with RPM. This rise reduces the current flowing and is why the torque falls off with RPM and why the RPM is limited. All electric motors do this, its just a question of what RPM and steppers are generally lower.
Like everything, counter-examples to generalities exist but its more a matter of matching your power-supply to the wiring than anything else.
Cliff |