I've got a reel that only holds about 150 yds. of backing which should be enough but I'd like another 75-100yds for insurance. I would have never thought I needed more until I recently got 1/2 the backing ripped off my Tioga in a few seconds. Part of the reason of having a large arbor in my bag of tricks is that when I did got hold of the handle and started to retrieve line I was probably getting 3-4" per turn of the crank, resulting in a lost fish (whatever it was).
I'd like to hear from any of you who have used the super thin backing and what you think of it.