DxOMark just tested the Nikon Df, and the results are interesting. The Nikon Df is a DSLR that looks like and in some ways is set up like an old film SLR.
What is interesting about the scores that DxOMark gave the Df is that the camera has the best high ISO performance from any camera they've ever tested, including the D4, which shares the same sensor. The Df is the new king of digital high ISO.
What is also interesting is that the color depth and dynamic range scores are identical to the D4, which means that both color depth and dynamic range are very good, but not great.
DxOMark test scores don't necessarily mean anything. It's important not to read too much into them. But what can be gathered is that for high ISO, you won't find a better camera. If you do a lot of low light photography, the Df may be the right camera for you.
If you don't do a lot of low light photography, you may still like the Df for its SLR-like styling and salute to the days before digital. If not, then the Nikon D610 is probably a better choice, or even the Sony Alpha 7R.