I own a BMW X5 Twin Turbo diesel myself, I love diesels.
I know BMW is capable of towing massive loads, however nothing compares to the capability of a Volkwagen V10 TDI.
I know this thread is about BMW but I am excited about diesel power.
Watch a V!0 Diesel tow over 200 tons. A full size Boeing 747-400
https://www.youtube.com/watch?v=WmM-635RR6o