If it's comfort you're after, the X6 asks you to ask yourself: comfort for whom? Up front, the X6 is every inch the luxurious SUV (though you'd be hard-pressed to tell it from a BMW sedan if you weren't paying attention when you climbed into it) and comfort, materials, and features reflect that. In the rear seats, headroom is at a bit of a premium, though it can fit even taller passengers if they're not put off by close spaces.
Fit, finish, and construction are all top-notch, and that's reflected in the amount of noise that seeps into the cabin: not much, until you get the wide tires and large side mirrors toward the upper end of freeway speeds. The cargo area isn't vast, restricted by the sloping roof, but it offers more space than a typical sedan--back to defying categorization. Visibility, especially rearward, can be a difficult due to the narrow glass areas.
The X6 has 59.7 cubic feet of cargo space with the second-row seats tucked out of the way, but the X5 adds 25 percent more room for a total of 75 cubic feet.