And who said Range Rovers are perfect and never do a not-so-briallant system? HDC seems to operate best in moderate slopes with uniform texture/topology, like a stretch of sand or a stretch of pebbles of the same size, etc...
I don't know about the post 04 improvement, but i am almost sure that no electronic system can negotiate a really steep rocky desent... in such cases you have to litteraly go inch by inch with occasionally comming to a total stop in order to avoid building kinetic energy that can make you slide all the way down like a folling rock...
The tougher the road is the less electronics you want to use... even the DSC should have been turned off as the guys said above... and if you really want an off-road vehicle, it should be manual transmission, but we're not going to the extreme here... Just this DSC seems to be handy in some really specific circumstances (maybe around 10-20% of your offroad adventures)

__________________
BMW X5 3.0si 2008
Premium Package
Light Package
Navigation
Reverse Camera
Rear Sensor (retro-fit)
Comfort Access
Spare Wheel
Power folding mirrors
Voice Control w Bluetooth
Power trunklid

BMW X3 3.0i 2006
M Aerokit
M Sport Package
Navigation System
BT Handsfree
Xenon HID

BMW X5 3.0i 2001 --- SOLD