>>...at least one source mentions that an overly large colony (30,000) may actually fare worse in winter due to overheating.

Or rather due to overconsumption of stores when broodrearing resumes in mid-winter.  I think the feral colonies that overwinter best are those that, with a big population in the first 3/4 of the active season, swarm and put away big stores of honey and drop the population to an optimal* size in the 1/4 of the season as they back fill the nest with late summer/fall nectar.

Waldemar  

*for a given area

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