Ok, my second post.

I have been watching the provided demos,

all Joints like shoulders seem to contract pretty well.

I have successfully dismembered a few.

However...

On those demos, you can see a few moves, like the serious 1-o-ones where the joints seem to move faster than I can make them.

Then I read from an outside source you can alter the speed that a joint will contract or relax, putting more force behind the movement.

Someone please tell me that is fake,... or am I missing something

It's the technique that matters. I suppose you can alter the speed of the joint, but you have to mod it, which is not a good idea considering the fact that you'll only have it for yourself and single player.

I suggest you learn how to build momentum in order to produce faster movements.

A lot of focus about momentum. I guess it takes far more time than I could ever imagine..

This is tough. I'm not quite sure if the joints move actually faster. I think they need the same time to extend/contract. But in serious replays almost all joints contribute to your movement so their power adds up and increases the speed your Tori has.
For instance: A pec needs probably (no idea) 35 frames to go from extended to contracted. If you make a crappy move your arm is slow and the distance he travels within those 35 frames is small. If you have all your joints contribute to the movement, part of the hypothetical moved distance adds (like using your chest or ramming your leg into the ground, it doesn't move but provides movement for your whole body) to the power of your move. So within the 35 frames of contracting pec your arm travels a farther distance and is therefore faster.
Hope you understood what I think. It's just a theory I didn't test it.
Don't want to comment on relaxing. My opinion is diversed on that. Might be possible a relaxed joint can move faster. Not generally but sometimes.

Type '/set ed 150'

Type '/sm 1'

contract left elbow, space, observe speed

newgame
contract left elbow and pecs, space, observe speed

As you can see, the second scenario has faster movement.

And to answer NutHug's question, when you edit a replay with notepad, you will see a line called ANGVEL. That line is the speed of the rotation of a joint. That means, a joint itself, can vary it's speed.

The speed of the wrist is different. But the elbow takes the same amount of frames to contract, counting from first movement of the elbow till last.
I explained the ANGVEL part. The elbow travels more distance in the same time and therefor the value is higher.

Basically, to get your body travelling at a high velocity, you need to have a good build up; being relaxed is usually regarded as being better and more aesthetically pleasing.