studless snows on 16" 05 wrx wheels.
typically switch around april and november.
the oem summers that come on the 09+ wrx's aren't that great in the cold. I started having traction issues around 35-40 degrees. It doesn't occur much, but it does happen. I would definitely NOT recommend using them all winter. The occasional cold days will catch you by surprise. I had abs kick on while driving at relatively low speeds multiple times in the dry when it was cold.
If you don't ski or board, and won't be in the mountains in the winter, maybe just get some all-seasons.