Just size. As long as the load limits are in the same range you will be fine. I should note that the picture above with the rims sticking out past the fenders can't be M5 wheels. I would bet they are M6 wheels.
Get what you want, but a 275 tire on a 10" wheel is at the small end of what will work. Again, the 255/35 295/30 is the optimal fitment for the M5 wheels on an xdrive car.
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