Thanks Peter, it's looking like I'll be going for the D600, 610, 750, 780 range as I would like video capability wich the D700 doesn't have, and my budget probably won't stretch to the D800 or later pro models - although, from what you say, I think I would probably prefer the controls on those models.
If I can just clarify your earlier remarks about DX viewfinders having improved - but does the image appear bigger, as it does for instance with a run of the mill 35mm SLR? Or is it still small as on my D70?
Actually as to cost, a used D800-D800E-D3s,(all video capable) all cost about the same as a like condition used D750. A D810, a little more, a D610 quite a bit less in the used market here.
When I wanted something with more dynamic range than my D700 offered, I looked at all the above carefully, and for months before choosing a D750. Video is something I don't consider, I don't use it, I bought it for it's low light capabilities and it's well rounded features. Even though I prefer to use a D700, I find myself using the D750 at least as much. It's probably Nikon's best over-all DSLR for the money. I much prefer to use a D700-D3s-D800 series, but at the end of the day the D750 just does it's job well.
I recently photographed several original Civil War muskets in detail, a lot of shots, some macro. I set the D750 on AUTO with a Tamron 90mm f2.8 AF Macro lens and got through some 250 shots, (over three days) without tiring of it. It would have taken quite a bit longer with one of the D700's!
Here are two photos that look unimpressive, but maybe not possible with a camera of lesser dynamic range. Taken on the Gettysburg Battlefield this April with the D750. The building is the Brian house which stood on the right of ''Pickett's Charge'' July 3, 1863. The fighting took place within 20m of the front door. It's locked and the only way to get a photos of the interior was through the windows, and on a bright day outside.
As you can see, fingerprints on the glass, spider web, and a crack. I put the lens right against the glass and shot. The lens is an old Nikkor 20-35mm f2.8 D
This window was a little cleaner.
The exterior and the two windows I shot through. The monument of the soldier was the Union firing position which extended into the field in the near distance beyond the curve in the road.
I would say the D750 is a very capable. It's not the Pro level tanks the D3s-D700-D800 are, but I believe it to be more flexible with it's dynamic range, tilting screen, and up-dated processor, one of the most well rounded DSLR's in it's price range. I have mine set up to mimic my D700's close enough that I get bye although I would still rather shoot with a D700 controls.
I would really like to try out a Nikon Df, (no video) or a Z fc, (video, but APS-C sensor). They should be like shooting an FM2. The price of a NEW Z fc is about what a used D750 is, but you would have to buy a ZTF adapter for F mount lenses, that adds $200.00 to the price tag.
You know what you need better than I do. If it's within your price range, I think a gently used D750 will do what you want and more.