I think its location based, period. Where I am at in CA we had temps in the high teens/low twenties last winter, but hovered around the 30's as lows. I have a ventilated inner cover and a SBB that was left uncovered all winter..............not a single loss of a hive. They also didnt burn through their stores..............of course Eucalyptus bloomed in january and the temps were foragable, so that was great!!
Although I like SBB, im going to solid two hive pallets for ease and moving to migratory covers as well.