SHMBO got a new BMW X-drive (AWD) last year and this is what we went with (Studded General Altimax Arctic in 205/55-16 instead of the 225/45-17
that the OE sized summer's were). By the time everything was said and done the package was ~$400 cheaper to my door from the Tire Rack than local pricing.
Some of the testing I have read showed studs improve ice traction by ~25-35% (compared to the same tires without studs), but can give up ~5% traction on dry and wet roads. I am much more concerned about getting the most amount of traction in icy conditions compared to a minor degradation in traction during dry or merely wet conditions so I am a studded tyre kind of guy.
BC and especially the lower mainland seems to be much more strict in regards to studded tyres than Alberta though.
I noticed the screw when I took the picture as well