I nymph with all my rods. I just adjust my cast depending on how big of a nymph I have to use. I can sling large double bead stones with my 3 wt if necessary. The only thing I adjust for is size of the water and potential size of fish. I do know that the 9'6" and 10' lengths in 3 and 4 wt are very popular for Euro-nymphing nowadays.
I do not do much of that though.
I would say a 9' 5 wt should cover most trout waters...
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