Hi,
You'll be just fine with those sizes. The reason you want a narrower Winter Tire is so you place more weight/inē on the ground. This smaller Contact Patch gives you better traction and control. For even greater traction, you might consider having the Tires
Siped, see:
http://sipers.com/sipers/index_large.asp Hope this helps...
Happy Motoring!...Jim'99