I don't think you would have a problem with a 5 over 5 nuc going through winter. We had 5 frame nucs going through winter and coming out very strong in spring with no medication except some HBH for nosema as it is my major issue with over wintering nucs. I put mine in insulated full boxes (divided) with a top holes for moisture escape, put some candy on them in January here ( just in case) and have them go into winter with 90% full of stores with a late summer queen. We came out last year with approx. 18% loss.
We used to winter nucs 5 over 5 with 13% losses but can double our wintered Queens in the same amount of space.
I use styro boxes with ply tops and bottoms but stacked 4 tall with a 3 inch styro on the top one.
We are in Calgary and the temp gets down to -40C for periods, but we also have days where in can be +10C from Chinooks and the bees enjoy a good cleaning flight. We have 4 inches of snow in the past 2 days, longing for spring!!!!