I am sure this will just be noise but I drove my X5 with OEM all seasons and also winter setup/summer setup.

The difference between the All Season and the Winter tire is HUGE. I am running Pirelli Scorpion Ice/Snow(255/19's) for my winters. My OEM all seasons could get me to and fro but with the Pirelli's the car never slid and the car stopped on a dime. I no longer had any torque steer when going around the corner. The tires grab like crazy.

On another note, winter tires which are meant for below 45 degrees have "400" tread-ware which from past experience on X5's mean they do not ware. See about 2/32 ware a year on my winters (on my E53 and E70) which you can run them a long time. What I found is running winter/summer setup cost no more than running an all season setup but I get better performance with the winter/summer. The only difference is I had to pay the money for my winter setup upfront instead of waiting for the All Season to ware out.

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2012 X5 50i ZAP(2VA, 336, 465), ZTP, ZPP, ZPS(6VC), ZCW, ZRC, 322, 4UB, 4NC, 610
2011 ///M3 Silverstone II
2011 X5 50i(lemon)
-- SOLD --
08 550 Msport
07 X5 4.8I sport
04 545i sport
02 4.4i sport
01 540I M/sport
00 SL500
97 SL500