So the way this thread goes, we're talking about the winter 2 years from now, right? In that case, might be worthwhile to take global warming into account, and there may not be any more snow...
Do you know anyone who has a truck with a locked rear? If so, would they let you try it out in a parking lot or so?
That said, I'd go for the 14sf. My first choice for traction aid would be an ARB (and I speak from experience, having had an ARB in the rear of my K5 for 8+ years); second choice would be a locker as I'm not sure how much use a limited slip/posi would be on the trail, considering your front is open.