Upgrading my D200. D7100 or D600?

[CR88]

Originally this was going to be an easy decision. I need to upgrade my D200 and add a wide-angle lens. So, I was going to grab a D7000 and a Tokina 11-16 f 2.8.

When I went to the camera store, however, to price things out, the salesperson, who I have worked with for many years, suggested that I go with an FX camera and put the money I was going to spend towards a D600. Her main factor for the suggestion was my preference for low light capability.

My current lens setup: Nikon 18-200 AF-S DX VR 3.5, Nikon 50 mm 1:1.4 D, Nikon 28-80 3.5-5.6 D and a Tamron 70-200 2.8, all DX lenses obviously.

The samples I have seen from a 7000, let alone the 7100 were so dramatically different from my 200 that either would be a considerable upgrade at the higher ISO range.

While I will be using this for business, there isn’t enough money in it for us to justify the expense of a $2k camera AND all new lenses.

Also, I do not beat on my cameras, although limited exposure to some of the elements does occur (mostly light rain and some snow) so I think that the 7100's body would work. My 200 looks and functions like new and had it not been for its limitations in low light, I would only be looking to add some new glass.

Since I have read conflicting opinions concerning DX vs FX with DX lenses, I am not sure if the leap to FX is right for me, especially since I may have to upgrade all of my lenses over time. Some say that I will still get better performance with the 600 even with DX lenses, and others say not so much.

If I could use my DX lenses AND get better performance than a 7100, I would make the leap to the 600. But, at this point, I think I need a few more opinions or clarification before I drop $2k.

Any input would be greatly appreciated.