Regarding your original question, I agree with everything that's been posted. With a 12V motor of the same torque capacity, the increase in current draw would be even greater. O scale manufacturers, in their slavish devotion to outdated NMRA standards, are throwing away the better performance that's potentially available by using 24V motors and power supplies. Of course most folks use some type of command control, so maybe it's a moot point.
You could test our collective hypothesis by switching to wider curves. I guess that adding more cars to the train would tend to even out the current draw. Running the loco "light" without a consist would cause average current draw to decrease, but I would guess that the variation as a PERCENT would increase, since the added friction from the loco's rigid wheelbase (flanges, and rubber tire, if your loco has one) would be noticeable as it abruptly transitions from the tangent to a circular curve. Good topic!
