I drove the X5 like I drive my M3

Ok, I guess that doesn't mean much, but I think it says something for the handling of the X5.
One thing I don't think people mentioned, and I'm not going back to check, don't drive past your comfort level, period. If everyone is going 80, and you're scared shitless going 75, do 70... who cares. It's your life, not theirs. If the car is wiggly, or you feel like standing water keeps breaking traction, slow down. And no matter how great your tired are or how well you know how to use/take advantage of AWD, it all means shit when you hydroplane over standing water or ice. Then it becomes a matter of sense, like B-Line said, and not slamming the brakes... but I'm sure we all know that anyway
And speaking of tires, I need some new rubber

Hurray for 225(235)/40-18s @ $200 a pop.