Well guys, I always put as much backing on my spool as it will take. I see my backing more often as I fish the Tongariro, the fish are often 20+ meters away so an initial run of only 10 meters will get me into the backing. It is not uncommon for a fresh Tongariro Rainbow to run downstream as much as 2 or 3 pools, and if you cant keep up you are going to need some of that backing! Some of you may remember this is how I smashed my elbow a few years ago, running on cannon ball sized bolders is not as easy as it looks.
It amazes me how often the trout will stay in the same pool and slug it out at close range though.
All the best.
Mike