Howard, man you are a lot of work.
Just kidding. Seriously, there are a lot of factors involved that make the motor do what it does. You seem to be interested in the efficiency aspect and unfortunately that is an area that I am not very knowledgeable in. Looking at efficiency as a means to get more usable power is probably not going to net very much. Here's why:
The commutator and brushes are the means to pass current to the windings. The windings are what generate the magnetic field that when pulled against the permanant magnets make the motor rotate. Create a stronger magnetic field in the windings (more voltage and/or higher current) and/or use stronger permanant magnets and you will have a stronger motor.
So..... What's really making our motors faster is the ability to have 2 strong magnetic fields in the motor. The power a motor produces is a result of these 2 magnetic fields and unfortunately you cannot force one or both to be stronger. The magnet is what it is. The armature has a certain number of winds (27 turns of 22 gauge wire for example) and this will draw a certain amount of current which will create a certain strength magnetic field in the windings. All you can do is make sure that the commutator can get as much current and voltage that it can via the comm and brushes and call it good.
I won't get into timing here but for the sake of discussion let's just consider it a non-variable parameter.
About the motor spring test... Well, I'm not so sure how applicable it would be in real world applications but the increas in efficiency likely came from lighter springs having less drag on the comm - less wasted energy basically.