Clearly the field coil is smoother and more extended, surprisingly (or not?) most at the bottom of the FR.
Logic should suggest this conclusion as lower frequencies require larger pulses of AC current to maintain a given acoustic output. It makes sense to me that it is in these critical low midrange frequencies that we would most likely sense(hear) differences that could be directly attributed to the reluctance and saturation characteristics of various motor types.

Beyond that, i just think it'd be cool to have a nice rack of glass cased wet cells to energize my speaker motors.