You look at the performance capabilities for your area. I talked with some SAAB owners who had M2's on their cars. Also talked with some people about Blizzaks and Michelin Alpins for feedback. Tread life in winter tires is limited depending on the road conditions. The drier the roads the shorter their lifespan. You have to think Ultra High Performance Summer tires and how long they last. It boils down to your individual style of driving. Most higher performance tires, summer or winter will only last 1 or 2 seasons at best.
HERE IS A PICTURE OF MY TIRES
Notice all the extra siping (the little squiggly cuts in the tread), these help the tire grip better in icy conditions. The tires are also made of a compound that doesn't harden up in the winter. I already had noticed my summer tires getting stiffer when the weather was below 50*F and got even harder as it fell. They also started giving up traction.

All Season Tires are a compromise, they try to do everything. But in order to do so they must give up something on the extremes. Most drivers feel that it doesn't matter because they don't take their cars to the limits and Ultra High Performance All Seasons are the most tire that they would ever need.