This is a great question.
But the answer is, in my opinion, one of the mysteries of fly fishing.
Over the years I have searched for the perfect Nymphing rod.
Every length and line weight was tested and many got close.
Then I found the answer by chance:
A Shakespeare Nymph International, Black colour, Brown bindings, not much to look at.
10' long #8/9 rating, material glass.
Unbelievable, typical glass but without any recoil, I would not call it backbone but positive when straightening the rod.
After a year or so the stripping ring required a but of attention and I sent it down to Mick Glover( formally of Perth) to be refurbished completely.
Mick loved the rod's action, could be used for almost any type of fish.
When stripped, shock/ horror- not glass at all but a composite of glass and something(has to graphite) but no, probably Boron.
Anyway a great rod for all fish but for all forms of Nymphing just perfect.
Shakespeare have no records published of this rod but the double tipped bindings suggest the USA as a source.
Nymphing rods are so personal, I hope you find yours and Tight Lines.
Ps. Mick will finish my rod early in next year.