I also use all mediums and live in Northwest Wisconsin. This is a busy time for me and my bees as we both prepare for winter. Starting next week each hive gets a complete top to bottom inspection which also entails removing all remaing honey supers and any empty frames and/or supers and basically just squeezing them down to a max of four mediums, although I've wintered over in 5 mediums with a big colony and no less than 2.
Upon closing up, each colony will have at least one full super of honey above the 1, 2 or 3 broodnest supers which are also surrounded with honey/pollen, less on the bottom super (perhaps as few as one frame per side) and increasing the number depending on the number of supers (I've successfully overwintered in as few as two mediums and as many as 5).
I make sure the top super is packed w/ honey and the inner cover is placed on top with another empty super on top w/ the cavity filled with 5-10 lbs of dry sugar for insurance, a 2" piece of rigid insulation over that, cover, wrap and done.
That all said, I'm going to try some of the advise gleaned in these pages and try some insulating of my hives this years...we shall see.... :-D