I have an opportunity to buy a Black Sapphire X5 or Titanium Silver X5. Silver is a nice and safe choice, but my wife loves the Black and it will be her primary car. I've always sworn never to buy a black car, but the Black Sapphire, given that it is metallic will probably show less swirl marks. I plan to keep the car at least 6 yrs...any feedback on the longevity of the Black Sapphire? Am I crazy to consider this?