I'm buying four 20" OE front wheels, buying four identical tires and using a spacer in the rear for looks. Looks good and will allow me to rotate tires through all positions. This method works well with my M5. Staggered fitments are an absolute bewilderment to me on these vehicles.

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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