Well, it is really hard to see out of the back. But, with the reversing camera and big wing mirrors, it's not as big of a pain as you might think.
As for the engine choices, the six-cylinder is noticeably nimbler and nearly as fast. Lack's the V8's turbo lag too. It's the one I'd go for.
I didn't get a chance to drive one without Adaptive Drive, but that and the Dynamic Performance Control are kind of the car's raison d'etre, it'd seem a bit pointless getting one without either.
Also, I don't know about the aluminum window trim on the six-cylinder or door step. The former looks pretty good in black and the car's not hard to climb into, despite its massive size.
The first part of my review is up here:
http://jalopnik.com/376456/2009-bmw-x6-part-one
It's a cool car.
Wes