Their were some guys that took a Z3 M coupe up the Dempster Hwy and all around yukon territory. All they had was a flat tire, and they had two spare tires on a huge yakima basket rack.

It's over at expeditionportal.com. I think an X5 should be able to handle itself. But spare parts would be a good idea to bring (outer axle joints, boots, steering parts, and tire service kits. as well as any filters and fluids)

I've done 85k miles offroad in a 2001 4runner all around that area and northern Alaska (north slope) and Central America/Mexico.