I agree with others that the skills and attitude of the driver are far more important to safety than the vehicle being driven.
As far as the vehicle itself, a few years ago I had a customer who owned one of these cars. The car itself was very impressive: quite large on the inside, comfortable, smooth as glass and powerful without being overwhelmingly so. It also felt rock solid, which makes it feel very safe. That car was eight years old the last time I worked on it, however, and it also had 100k miles on it and needed some pretty significant repairs. Brakes, tires, and suspension components were very expensive for that car, and the owner kept declining the work because he couldn’t afford it. The guy always had tools, a hardhat, and an orange vest in the backseat, which seems to indicate he was a construction worker. The 740i is a safe car for its time (maintenance and repairs will maintain this safety), but a newer vehicle with modern safety features will probably be safer, although less luxurious and less fun to drive. Almost anything, however, will be cheaper to own, maintain, and repair than this big Bimmer.