The most rod I have ever used for them is a 10 weight 9.5 foot fenwick glass which I built just for the kings. For the fresh 15-20 pounders using 15-20 lb test leaders it was sometimes not enough.
This was primarily on narrower rivers though with our omnipresent log jams in every hole and bend pool.
Its amazing what small caddis, stone, and hex nymphs they will take at times when nothing else works. Size 6-8s. Many times it is the hook which fails via bending due to the immense pressure you can place on them with a 10 weight and 15-20 lb test leader.
I don't care if I land them, so losing them is not an issue. Caught and landed enough of them over the years.
Now everything goes back.