First....lets address the "guys from Vermont". The guys I know, will privately tell you that anything over 50% in nuc overwintering rates, is considered a good year when factoring all the good and bad years. And all the "guys in Vermont" have been killed in the past few years with massive losses in one year or another. Of course, I don't see them hanging out telling you that on forums.
Personally, in a mild year, I can get through 80% of my nucs. In a harsh long winter, I may lose 80%. And I'm not afraid to state that when it happens.
I will pass this along....I have found out that the winter success rate greatly improves if you take the 5 over 5 nuc arrangement, and place the 10 frames in a 10 frame box. I think in harsh winters, the narrow walls of the nucs, and the cold being too much on the outside walls of the nuc, it really compresses the cluster to just a few frames.
If I take the 5 over 5, place them in a 10 frame box, slap enough fondant on top that they will not starve, I can get through a very good number with no problems.
Overwintering nucs is not an easy task in the true northern climate. I don't care what your knowledge, experience or technique may be. All serious nuc producers that overwinter large numbers of nucs have good years and bad. Even when they do the same things every year. And anyone stating otherwise probably is not telling you the truth.