I have a 4.8i, with the 20" wheels and run flats, that aren't m/s rated. I debated long and hard whether to get a set of 18" wheels with pirelli scorpion ice & snows.

After much thought, and realizing my front tires are getting near the end of their tread life, I went with 20" Toyo Proxes S/T, which is the only tire manufacturer that makes a tire to fit the rear that is M/S rated. Popped those on, and love the look - gives the X5 a more aggressive mean look.

Went up to Lake Tahoe from 12/21-12/31, and was able to enjoy two small snow storms.

My report: whether in snow packed or icy roads, the X5 had no trouble. Felt extremely stable, and I had to disable DST & Traction control completely and gas the car to get it loose. With traction control on, was able to easily get through snow drifts, and climb any hill with no trouble.

After having a Toyota 4 Runner with locking differential and BF Goodrich All Terrain TA/KO (True off road M/S tires), I've found the X5 every bit as capable in the snow and for any '4 wheeling' I ever do, despite having these wide 20" performance wheels.

For what it's worth.