I completely agree on the jump from D90 to D600, and in my case from D80. Megapixels are actually a tiny bit higher in DX for me on D600 and IQ, DR, DOF, low light (used to hold it to ISO 800 and cheerfully now go to 3200 and up on D600) are rather amazing. Weight about the same (seemingly) and controls not terribly different.
BUT: the D7000 is a heck of a camera and Costco has IT on an amazing deal about now as well. $550 manufacturer’s discount** is valid 12/16/12 - 1/5/13. While supplies last. Online Price$2,049.99 Less-$550.00 Your Price$1,499.99 Features: 18-200 mm VR Lens, Nylon and Leather Bag, Tutorial DVD, Guide, 16 GB SD Card, Twin SD Card Slots
YOUR decision depends on shooting subjects and lenses already owned.