it deppends on what you want in a car also... a 530i is powerful enough for me and more powerful than most of the cars on the road, but if you want an absolute beast you want a 540i. cost and maintianance is going to be the same. the only diff will be the gas milage. But that also depends on your driving style, for example my car is supposed to avg around 22 MPGS, but i get allot less than that because i drive crazy and race all the time. but it can also get good gas milage if you drive it like its supposed to be driven, for example i made 475 Mile trip on one tank.