Lucky, its my understanding that it is a "wild type" of the heartnut (which is a type of japanese walnut or no?). There is one thing that seems consistent, the juglans produced isnt nearly as high quantities as others walnuts, or plants in this family. I have also read that it can produce in 3-5 years from seed. I cant find any practical experience though, just a few articles and sites that pop up no matter what i search in google.

Lucky - I find it odd that butternuts would die back like that in zone 6. There are a few up here in NW ontario that do fine. They made it in toronto, even with the winter that past.

North - it seems the tree isnt very popular over here. IT was tested and rated as "satisfactory" in some places in alberta, and apparently a few specimens in edmonton are noteable. IF it survives and does ok in edmonton, us in zone 4 should have some luck.

Again, there is very little online regarding care in the yard, or peoples experiences

2007 was a disaster - and a good illustration of how important it is WHEN it gets cold, as compared to HOW cold it gets. Butternut is noted for its cold-hardiness...but we'd had an exceptionally warm Feb/March - with several days in March with temps into the mid-80s. Things had broken dormancy far too early - I had pecans/walnuts/persimmons with 8-10 inches of tender new growth...then, 4 consecutive nights of temps into the teens, at Easter.
Killed a lot of things outright, some just back to the root collar. Big mature oaks/hickories in the forest here were killed back to their main trunks - branches larger around than my thigh...dead. Some of those trees are still dying off after that insult and the ensuing drought that followed; it's just taken a while...