Brian
I have a question about your statement about regulating temp up instead of out. On my first year, 2 deep 10 frame hives I am leaving a extra med. super. I figure this will give them a extra 25-30#s. Some have made the statement that its to much room for them to heat but I was under the impression that they only heat the cluster not the whole inside. To me leaving the extra food above the cluster in another medium seems to make sense. Do you see a problem with this?
To answer your questions:
I have yet to find anyplace, worldwide, that needs more than 2 deeps of stores, or the equivalent, to survive a winter.
The more space the more moisture is retained within the hive. A vent at the top, even a small one, serves to vent that moisture so it doesn't rain back down on the bees. One condensation reaches a given point it rains, wet bees on cold nights (or days) die. A vent at the bottom (SBB) and one at the top (Irmirie shim) allows the moisture to vent naturally and doesn't affect the bees warmth in cluster.
With a narrower space, such as an 8 frame verses a 10 frames, less moisture accumulates above and around the bees, less moisture means less rain. Less rain means a better survival rate.
Another consideration is the narrower the hive the smaller the cluster and the slower the consumption of stores. It is the moisture, not the cluster size that kills the bees. I've overwintered Russian bees in a 2 tier medium nuc hive and still had 2.5 frames (out of 10) of stores come spring although the cluster size wasn't much larger than a softball.
Hope those points helps you out.