Tire Rack Tire Test - Winter/Snow vs. All-Season vs. Summer Tires on Ice
Too bad they didn't compare studded tires, then we would have some real information. Oh wait, they did:
Tire Rack Tire Testing - Ice Traction: Studded vs. Studless
Okay, that was a surprise. How about some high speed tests? Car & Driver goes to Finland where they test winter tires all year round.