Tires are what it is all about. Put summer tires on a hummer and it will leave you stranded in the snow.

My 4.8is with Michelin Latitude all seasons is OK in the snow with stock widths but when I put on dedicated snows, Pirelli Scorpions in stock size I could climb steep roads in snow with no slippage if going easy on the gas.

I think the X5 is as good as any AWD SUV in the snow with no transfer case locking - they will all perform only as well as the tires they have.