Personally, I'd see how it goes, obviously depending on the type of driving you do.

Two winters ago, I had a TrailBlazer SS AWD 400HP with stock 255/50/20's on it and drove through some of the deepest Chicago winter snow you could imagine, 20 miles one way to work and back.

My X5 has the 255/50/19's on it, so I'm just going to to like I did before, and take my time and should be all good, although I know yours will have the 315's out back so you might just need to take it a little slow.

Personally, I never once had an issue with my AWD SS with 400HP, and I love to play in the snow.

The BMW X5 with it's advanced XDrive I'm sure is just going to be even better.

Just my thoughts if you want to save some $$$ and you can control yourself in the snow...