Torn at the moment between the to. Our little D40x has taken over 50K images and > than 220gb of compressed imagery. We have used the snot out of it, but it's time to upgrade. Other than our standard DX 24-55mm and 50-200mm lenses, we also have a Sigma 10-24mm wide angle. From what I understand, these lenses will still work with either camera but may experience performance deficiencies. We take a lot of pictures of the kids (of course) and a pile of landscape/outdoor shots. Other than that, the main differences I see between the D600 and the D7100 are just a few things. D600: Comes with a 28-80mm FX lense. Full Frame 1080p, 30FPS Max ~39 Focal Points Better low light performance. D7100: Comes with a 24-300mm DX lense. Not Full Frame 1080p, but at 60FPS ~51 Focal Points and can get into a kit roughly $450 cheaper. There are a lot of other differences, but am really concerned with the low light performance. I have taken many extreme iso shots full of grain with my D40X and would love to get some better low light photos with less noise. I also don't want to keep second guessing if whether or not I should have got a Full Framer camera or not. The other side of that conversation is that I really don't want to throw money where I don't need to. Anyone with experience with these two cameras would be greatly appreciated. Looking to do something shortly. Thanks gents!