I just replaced all four of my tires last week. I stayed with the OEM tire from Michellin - MVV4 Plus (255/55-18). I picked them up from tirerack for $187 a piece. I never had traction problems in NY's winters, especially the 26in snow storm last winter. I drove fine on the roads after being some what plowed and even in much deeper snow on the side streets. Overall it's a good tire and I was happy with the thread life. 4 yrs old at 40K miles with 6/32nds up front remaining and 8/32nds in the rears. I had a blow out which was caused (see link below) by a puncture otherwise I would have gotten a little more mileage but then decided just replace them now and go another 4 years. Just my 2 cents.
http://www.xoutpost.com/x5-e53-forum/...y-updated.html