Jerry-could the results vary with the rootstock?
An older couple up in Cass County asked me what type of apples to plant and I referred them to Huls nursery website and also Beier's Nursery (Grand Rapids). I recommended they look at only zone 3 apples. Their haralson(zone3) died two winters ago. These two nurseries jsut handle the common Mn. types and not the obscure varieties that many of us want to plant.
Random thoughts
1. I have an almost 30 year old bulletin from the University of Mn. and they had their own zone rating system with some differences in central Mn. for hardiness compared to the USDA zones.
2. I also wonder if zone 3 or 4 at the edge of the prairies is a different critter than zone 3 or 4 in the northeast US. Maybe we should be looking at the Canadian prairie apple program from years back.
Someone might have posted that Maple Valley is a bit optimistic in it's suggestions.
There has been a bit of discussion of apple hardiness on the Far north gardening forum, not the facebook page.