For a change and a little fun my friend and I swapped cars for a week; my RRS HSE Dynamic 3.0d for his X5 40d M Sport.
As I've mentioned on another thread I am an SUV fan and so as a starting point I think both cars are fantastic and would highly recommend either, however (and we agreed) despite them being approximately the same size, weight, power and identical gearboxes they are very different beasts.
The seating position is lower in the X5, this together with dashboard curving around the driver makes it feel smaller than the RRS. In fact my mates wife commented that the RR "is huge" and the X5 actually felt small to me, both of which are clearly perceptions rather than fact. The steering is more direct and a combination of the run flats and firmer chassis (the RRS has air suspension) make the X5 feel quicker and more of a 'drivers car'. As many on the forum have noted BMW tech is very intuitive and is probably the best...