There is not such a big difference between 4 seasons and winter tire: there is a HUGE difference. I spent the first winter with my new car's 4 season and I tought the car was shit on slippery roads. Last winter, 4 real winter tires and wow! Not the same car!
At a time, my mom and I had the same exact car. She didn't believe in winter tire so had 4 seasons. I had Pirelli winter tires at the time. I took both cars to a parking lot, after a slight storm had left 2-3 inches of snow on an icy packed snow base. I had to force my car into skidding with the handbrake while her's was going wild just by turning and releasing the accelerator at the same time. And that was at 20km/h! The test was repeated on a frozen lake, at 80km/hr. My car would skid but I could still control it enough to prevent doing 180 degrees. On a road, I would have still hit the ditch but, at least, I had a slight chance to select what I was going to hit. With my mom's car, it was "round and round" with even complete 360! It was impossible to control or predict where you would end-up.
Numerous times since then, when a traffic light pass to green and it's slippery, I see guys skidding and spinning while I just start and pass them like it was summer. Numerous times, on the highway, I see cars in the ditch when mine doesn't even slip when I stop to help them. These peoples mostly, 4 times out of 5, have 4 seasons tires...
It's been proven in numerous tests, 4 seasons becomes almost as usefull as "slicks" on water when the temperature gets to -10C (14F). It was proved that the best 4 season, at -10C was not even close to the worst winter tire in terms of traction and stickyness. CAA is not affiliated with tire companies and urge peoples to install winter tires. Some north europeean countries even have laws making them mandatory between certain dates. In Québec, such a law is currently being discussed.
As far as ecology is concerned, I'm ready to do my part, but not at the expenses of my life so, 4 winter tires it is for me. And don't use them until the thread wear indicator shows-up: they are useless in snow past around 70-80% of thread wear. Just thinking about all the peoples who don't believe in winter tires and keep even 4 season till the thread wear indicator shows-up gives me goose bumps... Inappropriate tires in bad shape... Brrr!