Fast
I agree, in a perfect world.
Ofcourse, when I read the horror stories on this board on both indy mechanics and dealers, one is even more interested in wrenching on their own car not only from economical point of view.
However, I think we should clearly point out that an M5 is no beginners car to work on, and even the smallest of jobs can go terribly wrong.
I once heard of someone misreading the torque display on a wrench, pounds and Nm confused, which caused trouble with wheels coming off.
Also, topping of oil, dropping the filler cap between the engine block impossible to retrieve without use of a car lift. Not everyone is completely stupid ofcourse, but have seen my share of armchair mechanics telling me or my guys whats what holding internet printouts in their hand.