Remember it's a sliding scale. At 7 degrees a summer tyre and winter tyre of equal quality will be the same (roughly). The natural rubber in the summer tyre is starting to literally have a hard time of it. As you move down this difference becomes more pronounced but 3 -5 degrees either side probably doesn't really matter. (winters at the higher temp or summers at a lower) In the dry I'd be surprised if the summer tyre ever really struggles. In the cold and wet the winter tyre works better buying you extra meters of stopping distance and in the snow and ice the extra edges of the winter tread pattern make a big difference. I'm thinking about putting some on my merc in the next 2 weeks. That way I have an excuse not to take the GTI out in the horrible salty snow. :-)
