Don't get the 5200! I have a 5100 and something I have come to consider IMPERITIVE in a camera is autofocus fine tuning. I don't believe the 5200 has it. The 7100 does. If you can afford the 600, you can obviously afford the 7100. Go for that. By the way, I read somewhere that Nikon has acknowledged the dust problem in the 600 so it might be worth your effort to try the 600 again. You'll have an fx camera and it has autofocus fine tuning.