I suggest the 4.6is kit, paint the door ding strips, and add aluminum running boards but leave the other trim black. That will give you a more silver look without overdoing it by adding the 4.6 kit and painting the remaining trim silver. To be honest, I have seen a couple of silver X5's with all the black trim painted and it looks good but not great, surprisingly. The stock front bumpers are a little too busy in silver. All of the recesses and cutouts are more pronounced in the lighter color. Also, the picture you show with the big ACS wheels looks good partly because of those big wheels and because it is lowered so much. The all-silver X5's I saw were stock height and looked less aggressive and sporty than the one pictured.

On a practical note, you always run the risk of chipping, cracking, and peeling when painting plastic parts.

My $0.02.

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