going back to the original question I'll put things into perspective. I have a 2008 135i and went to Cayuga last week. I had just done a service so my "kms to next sevice" light that comes on when you start the car said 25,000. After tracking the car the light said 20,000 so I did about 5,000kms worth of wear in a few hours on the track. That obv doesn't take into accound everything such as tires and suspension etc but that gives you a general idea.
But for the record, it's totally worth it!!