In these example SP is using Newton 1.53. So much improvement in performance will be made if it is upgraded to 3.13.
In the last example with the chains, joints are very flexible and cause the chains to stretch out. It would be nice if they were more stiff. Can you give an advice to make them less flexible, so they don't stretch out as much? There are many sketchy physics models with tank threads, with each piece connected by a hinge joint, but the threads are not stiff enough. They either stretch or with one good push using the pick and drag tool the chain goes crazy.
Here is another example to see NewtonDynamics and SP in action: