First, the easy answers - each species has a different growth rate, so even within one genus the rate differs. For the Evernia forking, see Bryologist 93(1): 32-36.
Another paper that touches on growth rate but is mostly biomass not length is Boucher and Stone, Ch. 29 in The Fungal Community eds. G Carroll and D Wicklow, Marcel Dekker NY. I also researched growth rates for my thesis, some of that is in Bryologist 92(1):81-94. But the actual length is not in that paper. But if you read that paper, you will see that you could go out and look at a branch, and look at the length of a species on the section of growth for each year, to get a very rough estimate. Unfortunately, telling Usnea spp apart is no easy task, and it would be tough to decide which tufted thalli will be come the long ones you are describing. Perhaps this is a project you should take on!!
I think if i were you I'd work on learning to tell the spp apart first... and that is tough. I am very slowly working on a little book that will help but that is not available yet. A similar book for Britain, is available from the British Lichen Society for a very small amount, called Aide Memoir for Usnea - just nice little sketches of the spp showing relevant characters. However, the spp that we have are not all here. Also, McCune & Geiser Macrolichens of the PNW is a super book anad will get you a long way into understanding Usnea.
And a cautionary note - don't expect to be able to ID Usnea by looking a photos on line - as you can read in the Forum, photos are great but don't always show the characters you need.
best, Daphne