Don't forget the price difference between X5/X6 has to account for the status and demographics of the 'intended customer'. Example: I drive a 550 sport. A 650 sport is a solid $10,000.00 more but really isn't a more expensive car to make, nor does it have any appreciable performance difference. But the 650 driver is older and wealthier. Same with X5 vs. X6. The X6 is the SUV for the 6 series guy. I have an 09' 4.8 I just got for my wife. I offered her the X6 3.0 and she declined. She said "It drives too aggressively". She didn't mean the engine. Its cockpit is tailored whereas the X5 interior is sprawling, the seating position reclined and coupe-like to the X5's chair like upright seating. You'll find yourself driving the X6 faster. So, that said, it's not relevant to compare engines and MSRPs. They are different vehicles for very different customers. I was going to do an X6 5.0 when my 550 is up if my wife didn't get the X5, but I would never have considered an X5 for myself because I drive too aggressively for it (*I've never driven X5 M or M sport). I hope the X6 does well. Its a groundbreaking concept.