Below is a quote from Floridata.com regarding pecan trees, Carya illionensis: "Hardiness: USDA Zones 5 - 9. There are cultivars developed specifically for zone 5 that can produce ripe nuts as far north as Ontario, and cultivars for the deep south that require 9 months to mature a crop."
And, as with any tree, it is imperative you know where the seed stock originates from as it can/will be the difference between success and failure.
We are in a zone 4/5 area and there are many butternut trees, Juglans cinerea. However, you are within their native range and there is a virulent canker that is, allegedly, wiping them out in native areas. So that may not be the best choice for long term success.
I do not have any experience with the Carpathian walnut, a hybrid of Juglans nigra (black walnut) and J. regia (English walnut), but would suspect a better winter hardiness than the English.
The bottom line here is check for seed stock origin. Ask specifically where they are from, don't just settle for a generic "Oh, yeah, they'll do fine."
Sylvia