Bit OT now, but my MIL has a 2008 X5 4.8, great car, and doesn't have massive wheels, but she has noticed that it isn't as good in the snow as her 2001 Lexus RX. The reason? The Lexus has narrower chunky tyres, the X5 has tyres that look nice, and would be great for scaring hot hatches around the 'ring, but aren't much cop in slippery conditions.
The X5 is a brilliant car, and with the right tyres / in the right conditions, it is very convincing, unfortunately many are driven by cocks. Same goes for RR Sports, Merc ML's, etc. many of which are supplied with tyres that are fully appropriate for 85% of the time, but that seriously let the car down when the going gets slippery.
I also saw some shameful driving from an idiot in a late model HiLux with big rims yesterday, but then there are people in every kind of car driving like morons in this weather.