I believe the LR version will do either.

I'm actually partial to using crossbars as it makes removal easier.

 

Another option is Voyager Racks, they are pricey but they do have an Aluminum version that weights 26lbs.
i had one on my LR4 and ill be ordering one soon for my Discovery 5.
you do need to remove the rails as this bolt right to your roof, but they are super solid and didn't had any complains.

 

Voyager is also working on a rear ladder for the D5. Said to stay tuned...