From experience on Porsche forums with folks who install winter tires on their cars, the sottozeros get mixed results. Some say they don't have good enough traction on the snow and wear out fast. Most folks lean towards Michelin. I have Michelin performance winters on my Porsche, PA2 model, and love them. They handle like an all season tire but grip like a snow tire. Ths is great for a performance car. Another option is the Michelin x ice 2 which is getting great reviews, but that tire is a full winter set up with softer sidewalls, etc. than the winter performance Michelin PA2.
It all depends what you prefer : ultimate traction in snow, but give away wet and dry traction and a more sloppy feeling drive with soft sidewalls; or excellent snow traction, but not best, and much better dry and wet traction and handling characteristics. Because we only get about 8 snows a season on average in Chicago and streets get cleared fast, I chose the performance side of the winter tire equation. If I lived in Canada or Alaska with constant snow on the ground for months on end, I would go for a full on winter tire like the x ice 2.
2013 X3 28i, AW, Chestnut, Sienna, ZAP, ZCV, ZCW, ZDH, ZPP, DHP, rear view, park distance, cargo net (Wife's)
2010 Porsche Boxster S (Mine)