I drove an E60 M5 just before I turned it in for an X5M. I needed the space for my kids. This car is almost as fast and grippy as the M5, yet manages to be more comfortable and usable. I took it on a ski trip where snow was everywhere. My dealer warned me not to go on snowy hill like other SUVs but, it managed to pull it off well. It had not ample but enough space for two babyseats and all the luggage and equipment for family of four weekend ski trip. The gas mileage is terrible, but if you have to worry, try HONDA. THis is not for you.
The handling and launch outperforms the M5 in cold weather conditions. Rear biased 4WD system or Xdrive does it very well. Definitely the choice over M5 on the winter. This car feels more like a Rear Wheel drive in cornering and snowy roads. Because of it, it feels less confident on snow. The ride quality is definitely better than the M5, It feels smoother and more comfortable without sacrificing cornering capability.
The fuel economy on this engine is better than the E60 M5's engine, however it is still very difficult to manage a 350 mile range. One reason being tempted to floor the accelerator.
The Interior of the E70 X5 feels outdated compared to F02 7 series or F10 5series. It is in par with E60 5 series which is one generation behind. The trunk space is ridiculously small for an SUV when you have third row seat option, which is not available with the X5M. The transmission, although faster than my other car 750Li, does feel out of place in the X5M. This car deserves the DCT found on the M3 or whatever they are planning to put in the F10 M5.
This engine again has the same problem of burning engine oil as the M5, but it seems to be at a much slower rate. If this is a problem with all BMWs, they should have a program to give out free engine oils.
As long as you don't mind the terrible mileage, it's an amazing car to drive. Wolf in sheep's clothing. To the casual observer, a soccer mom SUV, but it's as close to the acceleration of a roller coaster that you can get to.