This is how I understand the differences:
VDC and VSS both have 3 settings: Normal, Sport and Sport+ that have to be manually selected by the driver. I think VDC includes VSS because VDC effects both the suspension and the steering.
Perf Control and Servotronic Steering are both either switched on or off. They are both dynamic depending on the vehicle's speed and direction. PC dynamically changes the power to the wheels when cornering as described above. SS is as per
http://www.bmw.com/com/en/insights/t...rvotronic.html
I couldn't see enough advantage in getting VDC on a 2 litre diesel engine. On the 2.8 or 3.5 petrol, I would probably get it. I have both PC and SS on my order.