The best information to date can be found through the IIHS (Insurance Institute for Highway Safety) testing of front crash prevention systems released 5/29/14. They evaluated the 2014 X5 and found that with the active driving assistant and active driving assistant plus options, the vehicle reduced the speed in a 12 mph collision by 9 mph and in a 25 mph collision by 7 mph gaining it an Advanced rating. Most interesting is that with the active driving assistant, active driving assistant plus, and the adaptive cruise control (ACC), the vehicle avoided a 12 mph collision and nearly avoided the 25 mph collision. Thus, the radar system from the ACC makes a significant difference in the effectiveness of the system and achieves a Superior rating. In the high speed testing, this is better than Volvo's City Safety with the optional collision warning with full auto brake and pedestrian detection. The BMW system also had the same results for the 5 series. Individual vehicles can also be searched at the IIHS site, but here is the link to the status report:
http://www.iihs.org/iihs/sr/statusreport/article/49/4/1