As I may have elaborated already, the new type transmissions(including 6 and 8 speed in E70) by design perform much different than the old generations. It is much closer to manual than to a classic auto tranny. By default the torque converter is locked-up and will be unlocked in some occasions only. This behavior helps to improve fuel economy, but also keeps the tranny temps low. The greatest source of heat in automatic transmission is unlocked TQ and eliminating this element almost completely really makes difference. Eliminating the excess heat in the transmission eliminates the main fluid wear factor, making the fluid to stay fresh for much longer.
Generally, the factory filled fluid will be of the highest quality available. I'd guess depending on the usage it would be good for 80-100k miles and this is when I plan to change mine-frequent towing and a lot of power.