Adding torque on an object's axis


What I am trying to achieve is to have a cube that rolls around an axis caused by a torque. When adding the torque and increasing its value, the rotation increases linearly. After a certain value, it seems like the rotation of cube is saturated and its not moving faster with high torque (100 and 1000 torque causing cube to rotate at same speed).

Note: I want to rotate cube using script not through animation.

I am attaching script and Inspector screenshot.

Make sure to adjust this setting:

You could just rotate the object around a pivot without rigibody which is going to be more performant.
add a script to the cube containing something like this:

    public Transform pivot;
	public Vector3 rotation;

	void Update()
		transform.RotateAround(pivot, rotation);