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...