I wouldn't go with zero toe in the rear. Toe in provides stability. Stay within factory range on toe in at the rear unless you literally want to chase the tail of the X5...

Sorry, can't help on the adjustable bushings question.

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Kirk
Las Vegas
2016 X5 40e Mineral White/Black Dakota Leather, ZLL, ZCW, ZDA, ZDB, ZPP, multi contour seats, rear side window shades, HK stereo
2011 E90M3, 6-speed manual