Go for the Nikon D600, you will be really happy by its amazing image quality (same than the Nikon D800 image quality but using 24 MP instead of 36 MP).The D700 was an excellent camera but the D600 goes much further in every single area, even in high ISO pictures, and many more.Check the few postings here on the D600 and you will quickly understand that it is an amazing full-frame camera, at an ama