Eeeeeek!! dont forget the hub sizes are different on the rear axle of X6, X6M and X5M due to adaptive drive wotsits.
SO any X6/M or X5M rear wheel wont fit the std X5 rear hubs as the wheel will be 72.6mm centre bore and the hub 74mm , slightly more than an interference fit....
Spacers to resolve this may or maynot be available from H&R but this starts to play with offset and may stick the wide X6M rear rims outside of the wheel arch?