Interior bike rack versus roof rack

[sunc]

We're trying to decide which way we should go in terms of carrying our bikes in or on the X3. I'm tempted to go with the interior one because it protects the bike in the X3, no hit on gas mileage, and is a pretty specific thing to the X3. The roof rack makes more sense in terms of flexibility with other accessories (skis etc...) and I save on space inside the X3. Any thing else I should think about?

Another thing, I'd hate to be forced to take the bike rails on and off of the X3 if we went with the interior option (since you need to fold the rear seats down). Can I slide it through the ski slot (we have the winter package)?

Finally, does anyone know if the roof rack is similar to Yakima or Thule? Is it round or elipical (meaning I can use another brand's bike rails)? And does it make wind noise if left on the roof?

Thanks!