It appears that the hub sizes vary fore and aft on the X5M like the X6 being 74.1mm in the front and 72.56mm in the rear. That means I'd have to bore the X5M rear rotors to 74.1mm to fit my rear hub.

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8/2011 X5 xDrive35d Sport, Black Sapphire Metallic, Black Nevada Leather, Fine Burr Walnut Trim
2/2001 M5, Jet Black, Exclusive Complete Black Walk Nappa Point Heritage Leather, Black Cubic Trim