When you are selecting a winch line you should try to get a rope that has a breaking strength that is 1.5 to 2 times more than the maximum pull weight of the winch you are using the rope on. If the winch you are using the rope on can pull as much as 9,000 pounds then you want a rope that has a diamer that allows it to pull between 13,500 and 18,000 pounds.
The larger diameter of the line will increase the amount of pulling strength that it has.