What tire sizes are listed on your tire inflation chart on the driver's door/door jamb and/or your owners manual? What ever is there...will fit your X5.
The V8 M sport pkg probably has larger brakes which is why the recommendation is for 19" tires. This usually doesn't apply the the 6 cylinder models.
{tires with the M+S (mud + snow) designation is what BMW recommends for winter tires}
