http://www.dpreview.com/previews/nikon-d600
it has a good highlight summary on d600 vs d800, comprehensive image quality comparsion and other useful infomation.
from the review, i am very impressed with the d600 image sensor, especially, its high iso performance. as a happy d7000 owner, i have no concern over d600 other features, since it is pretty much a d7000 with a fx sensor.
another thing, between lens and body, i would put extra money on a pro glass without hesitation. not only, it holds value extremely well(much better than a body), but also has a significant impact on image quality and camera performance.
