So here is a grain weight window for Switch rods that is as accurate as it gets and can be utilized by most ,and I will say MOST cautiously.
Some of the newer companies have no idea and will simply grab at a hat and hope it fits.
Switch Rod Line stats
Once you enter the world of Two Handed Fly Rod Casting many things will change.. a great and obvious observation is the significant ranges in line weights. But you really have to carefully understand that this range is simply there to accomodate the various casting techniques. For Example...Single Hand Overhead, Scandanavian, Skagit, Surf, Traditional Spey casts,and modern. Now you see what I am referring to! As the word itself signifies,Switch..from One hand or Two Hand
A good and simple rule to follow is this..for any overhead casts needing reasonable excess distance use the lower number, if you are considering a distinct shorter stroke then the heavier line is required to load these rods deeper without compromising rod abilities and efficient re-coil and dampening. An overloaded rod will simply not re-coil efficiently and not react well to a serious overload.