Mark my word; GET SNOW TIRES! Tirerack pkg approx $1400.

 

This past winter was the first time I switched to all season. I heard that if you get in an accident during even a minor snow and the other person was at fault, you might be blamed for part of the liability because of negligence driving summer tires in the winter. I put on Ultra High performance tires with a "W" speed rating so I'm leaving then on year round and will put the summer tires back on when the car goes back off lease.
I do notice less traction if I am running 10/10ths in a turn (maybe 10/10ths come quicker though, don't know), but the break away is still predictable.

 

Here's what I did, and I live about 2 hours east of Chicago and get similar weather.

I got on Ebay and found a set of stock 17s sytle 138s with Continental snow tires that were being sold by someone who was turning in his lease. I got the entire set for $500, and there was plenty of tread left. You have plenty of time between now and next November to figure this out, so I would not go drop $1400 at Tirerack. Watch the classifieds, check ebay, and you'll find something by the fall.

Also, while you may only get 6 snow days a year, there are plenty of "slush" days and other bad weather when you will wish you had snows. Don't risk it. I took a pic side by side of my snow tread to my summer tread, and there is an obvious difference. I'll see if I can find it. Good luck

 

OK, I found the pictures. Here is a comparison of the tread of snows vs. summer performance tires:




Also, the summers are wider than the snows, which adds to their poor performance in winter. You want narrower tires in snow.

 

I live in Central Illinois with a 545i and sport package. I opted for the Tirerack tire/wheel combinayion of Blizzak WS-60s on 17s. Car runs great in snow and on ice. With this I see no need for all wheel drive.