We had a 04' E53 X5 which had 2nd generation x drive (1st gen. was 99' through 03' where the torque split was fixed at 38/62). Our 04' X5 was not that confidence inspiring in the snow compared to a 3/5/7 series b/c the DSC intentionally didn't kick in fast. BMW materials proclaimed that this delay was intentional to allow the 4 wheel drive system to pull you out of a skid.
We now have an 09' 4.8 sport and today was the first snow. The DSC kicks in much more quickly than the last X5 - which is a relief. Nothing worse than understeer plow going into a corner a bit too fast. As for the x drive, it had always worked well, it just seems a bit more seemless in the E70.
(BTW, my comparison is done with dedicated snow tires on both the old and new X5)
Happy motoring all.
DRP