Thanks for pointing that out. Would one method work better with a non-constant frame rate?
you should use a fixed time granularity, let say 10ms
if you have to simulate the physics for 30ms (because your last frame was 30ms ago) you just perform 3 physics loops : this is important for the correctness and stability of the physics simulation model.
this is important because using too bigs times steps will results in completly wrong result :
the fastest your object go (compared to its size) the smallest the timestep must be and more generally you should never move on atome more than half the lenght of the n constraints (springs length) it is connected to.
EDIT : this is why it is pretty hard to push such object with a huge force (still in comparaison of its mass & size), because such force will result in a hight cceleration and so a too big move