Braking on ice and snow is all about the tires and vehicle weight. Theoretically, an X5 braking on snow/ice would be like any other vehicle of the same weight on the same tires.

But what would I know, I haven't even driven mine in the snow yet. Just put on the new winter shoes yesterday - Pirelli Ice & Snow on 17s. My sister had these on her Range Rover and said they worked great in the snow, plus it sounds like a lot of people on this forum had positive experiences with the tire.

I'm pretty excited to test the X in snow (just purchased 2 months ago) and find the limits of what it can do. I've driven a few different vehicles in snow:
Lifted Dodge Ram 4X4 on off-road style M+S rated tires
Jeep Cherokee 4X4 on M+S tires
Volvo XC90 (AWD) on all-season tires
Toyota Celica (FWD) on street tires, with and without chains
Yes, I drove a Celica in the snow on low-profile street tires without chains. It was an emergency situation and I do not recommend anybody do this!

I'll see shortly how my X5 measures up and report back.

__________________
'03 X5 4.4i Sport