I have been using the D200 for many years and have always used DxO Pro as a raw converter. This software has excellent high iso noise reduction and I have hundreds of virtually noise free exposures at iso 800-1000.
According to your equipment list all your Nikon lenses are FX (I don't know anything about Sigma lenses). Therefore, I suggest you consider a second hand D700 which will give you noise free pictures to at least iso 3200. The D700 camera body has a very similar feel and construction as the D200. You can always retain the D200 as a back up or in case you need the longer reach. Another advantage is that the D200 and D700 use identical batteries and memory cards. I have been very happy with this combination for the past four years.