All I can say is: if you get the chance to do this, definitely do it! This event by BMW was the most fun I've had in a long while. Besides checking out an interesting direction the auto industry is headed in, I learned a few things about better driving and, above all, got to practice them in a safe arena.
The Roller Demo
This is similiar to MB's one wheel moving test, except their rig tested all wheels in a single-wheel w/ traction situation. The spokesman mentioned that only 5 vehicles can successfully navigate it: Hummer (if it fit and didn't crush the ramp :-), LR DiscoII (which has a DSC variant), JGC w/ QuadraDrive, ML, and X5. He also said Audi's Quattro would do it, but their cars don't have a big enough breakover angle.
The Competitive Demo
This was where they did an avoidance manuever (hard left lane switch, then right lane switch) w/ different competitors: LX470 and ML430. No outrigger on the X5. Afterwards, I talked with the rep/driver who was the spokesman for the demo. I mentioned that without an outrigger on the X5, it was probably not an apples to apples comparison. He replied that the X5 behavior was the same w/ the outrigger (I doubt this), so I suggested they might want to leave the outrigger on to show a true comparison. He also mentioned that DSC/ESP/VSC was turned off in the demo after I asked (but not in front of the other people who had left for the track demo already). The lame response when asked why was that they wanted to demonstrate the vehicles' natural dynamics w/o the assist of electronic gadgetry because the gadgets might fail (there is a reason manufacturers put the gadgets on in the first place: safety). One of the other BMW reps/drivers (it's important to note that all the reps were professional race drivers) mentioned that you couldn't turn off VSC on the LX470, so it had it on.
The X5 lifted a wheel (right rear). The spokeman pointed out that this was the best behavior (though I'm not sure why...I'd worry if this happened, and yes, I am not a VW three wheel salute fan).
The LX470 was totally out of control. It leaned hard on the outrigger. I forgot to ask what height position the LX470 was in (it has an air suspension that can be varied in height by a few inches).
The ML430 leaned on two wheels and hopped a bit. The spokeman mentioned that this was because of the ladder frame storing energy, so eventually it would do this, even w/ ESP turned on (but it was inconsistent w/ ESP turned on, so that's why they turned ESP off for the demo). He also mentioned that MB's ESP system brakes the front wheel first, whereas the BMW DSC system would brake the rear wheel in the same situation, and this also added to the hopping behavior. I think this hopping behavior is something MB should look at. I think someone on the M-Class mailing list noted the same behavior when he pushed a turn too hard w/ ESP on. The recent C&D ML55 test w/ the souped up MLs also had this behavior when they turned off ESP at high speed.
This was probably the most useful part of the experience. They gave us a quick rundown of how you have to be smooth when driving on the track and what causes oversteer/understeer, etc. The instructor taught us how to hold the wheel, when to brake, aiming for the apex, etc. If you've read Curt Rich's excellent Drive to Survive book, you know most of the material already. Learning and applying are totally different things though. I kept understeering. When put to the stress of going through the course fast, my normal, everyday, smooth driving turned into stomp the accelerator/brake, overspin the steering wheel when encountering understeer, etc. I did want to stay and keep trying until I got it right (yep, it was that much fun! :-) but they didn't let you do that. :-(
The track itself, was composed of chalk lines and cones on the air force base runway. The track pattern has a lot of curves, switchbacks, etc.; I never went to the MB ML event, but that one sounded more like a standard oval racetrack. Pushing the X5 hard was an interesting if not confidence inspiring experience. There was more body roll than I expected. Tire traction breakout to understeer/oversteer was hard to sense (though this could be because of the multiply curved track). I couldn't see the cones very well to the sides of the car. Steering w/ ABS felt really strange (lots of body roll). Most people lapped in 24sec and the instructors lapped a bit under 21sec. It was mostly a high speed steering test. It would have been interesting to put an ML through this; there's no way it would have done as well as the X5 though.
The X5's tires last 4 days worth of the event in case you're wondering how bad the curves were :-)
There was one interesting thing about the ABS practice they had us do first. The wheels actually seemed to lock up every half second or so. I had thought that w/ ABS, the lockups would be imperceptible to the naked eye.
The Hill Descent Demo
The interesting thing about this was that he brought it to the top (track that went over a semi-trailer) and then let it roll backwards in neutral. The HD system kept the speed to 6mph (you could see the wheels lock to enforce the speed). He then went through forwards, and HD kept it to 6mph w/o wheelspin. I'm not sure 6mph is slow enough. It seemed too fast if you go off-road or wanted to really avoid stuff on a steep hill.
Spun out (oversteer) on wet, slippery area w/ it turned off. Spun less w/ it turned on. I didn't see much of a point in this demo even after watching from outside the X5. It was a great amusement ride though :-)
Charity Demo Benefit
You could sign up for any BMW sedan/car and they'll let you drive anywhere you want (unsupervised). They donate $1 to a breast cancer for every mile you drive. This isn't performance/comparison related, but it is a nice gesture from BMW (trusting you and donating to charity) that I wanted to applaud. I wish I had enough time to do this.
I was very impressed w/ the X5's handling. I don't think a V6 would work well w/ it. It felt heavier than the ML but I thought the V8 pulled it through admirably. Most of the people I talked to didn't like the X5's price or trunk space. If they come out w/ an X5L or X7 as planned, it will be worthy competition to the RX300 and ML for those who are well-heeled S*U*V seekers (I doubt BMW will lower the price much). I didn't think it was more luxurious inside than the ML; the only things I'd really miss that's not on the ML is the multi-function steering wheel (and boy, do they have lots of functions on the X5's) and the hand brake. The rear seats on the X5 are too flat and not that comfortable; I slid a lot during the track portion. The brakes on the X5 are AMAZING; 60-0 in 117 feet...it felt like slamming on retro rockets when you kicked the ABS in by stomping on the brake. As it stands now IMHO, the X5 would interest people who want performance w/ a high seating position (and to have the latest cool auto in the neighborhood), but not people who want the utility part of an SUV because of the trunk space.