i rented the canon 5Dm2, a900 and d3x for a 2 week period. the $5k difference wasn't too much of an issue for me.
i liked the d3x the best in terms of overall handling and non-processed picture quality, but ended up buying the 5Dm2. for my fine art apps (low, artificial light), the raw images looked about the same...i spend hours and hours in photoshop and couldn't distinguish the differences in the end product (30x40 inch digital c prints).
Fair enough. BTW I don't suppose you know anything about the white balance algorithms used by Nikon et al? I think the flag ship cameras used to have a small incident light sensor on the top of the prism.