This post has produced some great discussion and input and is accomplishing what I really needed. It is making me think about a hundred things that I had not considered before.

Yesterday, I was just about convinced to go with a 7100 or 7200 because of the lens issue. At this time, I am leaning back toward the 610, 750 or 800 series. Although, my 17-55 (I initially said 18-55) is an excellent lens and is DX, it will still be useful. I also have a sigma 10-20 which is DX. I think I have a couple more older lens that are FX, but I have given some away and sold some as I sold off older cameras. I gave my D1 and a zoom to an aspiring young photographer at my church, and she has made great use of it for the past three years.

As someone pointed out, my Nikon 60mm is FX so that means I have at least four FX lens at this time with the Nikon 70-210, Sigma 150-600 and the Nikon 80-400 VR. I sold my 70-200 2.8 Nikon a few months ago, but I think it was DX also. Until yesterday, I hadn't realized that my 80-400 VR Ed lens is also FX. At least, I assume it is since it doesn't say DX on it.

So at this time, I am back to FX format. Not sure if I want to deal with the huge files of the 800 series since I send many of my shots via the web? Not sure that I don't want to give the large mp a try? Don't know if there would be any benefit in having an 800 and using it on a lower mp setting?

My initial thoughts on the 610 were to migrate to FX at a relatively cheap price and then see if I want to invest more. At age 68, I do realize that every iteration of technology may be the last for me. At least, I know I am much closer than when I purchased my first Nikon so many years ago.

I have been viewing the 7100/7200 as low on the quality chart when compared to the pro or prosumer models, but I was completely overlooking the fact that the 7200 is Nikon's current top-of-the-line DX format camera.

The Sigma 150-600 is the only lens I have that is designed for FX use, but I understand that all my other lens will work but not too well at the wider settings (vignetting).

The loss of using my 18-200 would be significant. It is not my best lens, but it is the one I use most for my walk-around lens. Maybe I just need to decide whether to get a 7100(Refurbished for $599) or 7200 (New for $1099)?

I currently have a D2X and a D200. Considering adding an FX format just for the sake of updating my really old technology and having the full frame format.

I currently have several older Nikon lenses such as the 18-200, 80-400, 18-55, 60m macro and a couple Sigma zooms including latest 150-600.

I am trying to decide if I want to go with a very nice D3 for about $1000 or a D610 for about $1500. I know the build quality doesn't compare, but I am wondering which one will actually produce the best overall shots for several years to come? The 610 has the advantage of 6 years of technology and 24mp compared to 12. The D3 is in a class of its own.

I have read hundreds of reviews on the D3, D610, D700, D750, D810 and the other lower priced versions such as 7100, so I am aware they are out there, but reading "about" and actually "using" are very different things.

I am a serious amateur at best and go through spells of taking many pictures and other times taking very few. I take shots any/everything including family, birds, landscape. Minimum sports. Had numerous Nikons over the last 46 years, so don't intend to change to Canon at this point in life.

I just received a response from the person who wrote it, and it was a case of using an unclear statement. Thanks for your responses.

This person said they had updated the D3 to a D4. They did not change cameras.

Is it possible or feasible to have a Nikon D3 updated to a D4? I saw an ad that said someone had done this, but I'm not sure exactly what it means. Was this a firmware update or does Nikon change sensor, etc?