the stretch will me minimal, if you can keep the length of the straps to a minimum between the hammock and the tree. my defense of such a statement? - I'm a fulltime hanger and use a loop of 9/16" climb spec webbing ~10" between the hooks on my stand and the hammock and have not had any problems with them stretching out. just remember that with nylon webbing the farther it is from the end of the hammock to the connection point of your tree the more stretch you'll see in the webbing.
i would also think that if you're always setting up in the same place go with it if it works for you, if not swap out to poly webbing.