The linked article claims "in dry conditions, summer tires have the best grip down to 0C", though, which doesn't seem to match where you suggest the crossover point is.
winter tires, especially the snow versions, are straight out a source of danger here in central europe.
i just put some snow chains in for the winter surptises, and ride with my summer tires because its grip is clearly better on dry and wet bithumen, even in near zero temps, which is most of the season.