I hope you were not offended by my "hillbilly" comment. Just trying to give you a hard time.
I think the first question is does HRE make the P40 for the X5. The P40 is my favorite wheel. I looked all around to find pictures of it on an X5 and found ZERO except for Photoshop. And I am fairly certain the largest they come in is a 22" so that option would be out anyways. A darker color like the ferric grey may make them look at little bigger than the silver.
I decided to go with the ferric grey 215. Matter of fact, just got them in last night. I love the look but they are outrageously heavy. 80lbs a piece! Curious to see if I can feel a performance hit with all of the extra unsprung rotational weight. Not sure how much the original X5M wheel/tire combo weighs.
I would consider the P40 in a grey in the near future. Let me know what you find.