I beleive i am well qualified to offer information on BMW bodycentre courtesy cars.
Generally speaking no, they do not offer amazing courtesy cars. Infact in the case of a fault claim against your own insurance, most actually have a small fleet of complete rubbish to satisfy the minimum requirement courtesy car of your cars insurance - my local one has a few Corsas (Not kidding) for this unless you personally opt to pay extra or unless you make an agreement with them prior to the car going in.
Amongst the better cars most do not have anything better than 1 and 3 Series with 4 cylinder diesel engines. The absolute best courtesy car I have ever had was a 320d M Sport, and I've had more 118d's than these.
It's nothing like Service where the loan cars can often be pretty tasty.