Cold low light non moving subjects

Simon,

I'm not sure you need as much camera as you think. Ultimately you need a camera with the ability to record bright objects without clipping.

You might be better served by spending your money to have your current images printed by a professional firm who has experience working with camera files. They will be able to extract the best image from your files, It is possible that you have a good enough camera. If not they can give you direction as to the best camera to overcome the deficiencies of your current setup.

If you feel the need for a more professional camera look into a used D3 or the next Nikon model down, I don't remember model, I think d800 replaced it though. If you prefer the Canon way, look to a used 5d mark 2. Again, I mention these cameras only if you feel the need for a camera body to reinforce the fact that you are a professional.

Mike