I’ll reply in more detail later this evening. Off the top of my head, I’d strongly consider the Icelandic landrace and experiment with crossing the Icelandics to the bankivoid gamefowl you’re considering. You can then see what does better for you there, the pure Icelandics or the Icelandic x gamefowl crosses.
I’m sure the gamefowl combined with a LGD will deal with the predators fine. What I don’t know about is the climate. American gamefowl have historically been kept free range in New England and the Midwest, where winters can be quite cold. But that’s balanced by hot summers. I have spoken to someone in Alaska who couldn’t keep RJF hybrids alive there not because of the winter but because of the cool summer.