I've never had issues with spacers on my M5. I've used 3, 5 and now 12mm in front. As mentioned above, not all wheels are rated for the X5. All my vehicles have 74.1mm hubs and whenever I've needed to, I've had a machine shop bore the hub opening out. Last time it was $200 for all four.

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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