A hybrid is being planned and should be available in 2009. Ultimately, you can get what you desire. If you are looking for fuel efficiency because you want to save money, I would go with the twin turbo xDrive35i, as you will likely save money on the actual price of teh car, which should offset the cost of gas later on. Hybrids are estimated to have shorter lives, as well, but I don't know much about this. If you want fuel efficiency to reduce harm to the environment, I would do a little more research. A lot of natural resources are used and a lot of damage comes from building hybrids. In my opinion, we are not ready yet to use them for mass production, but the car companies can't wait very long to make that kind of money.
Another option is the diesel-powered X6, which I believe will come to teh U.S. as well.
Regardless of your choice, be sure you get something you really like. I think that no matter what powertrain you decide to get, fuel efficiency and fun to drive will be better than that of your current Range Rover (which is also a wonderful machine in opinion).
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