amehta wrote:
Noise reduction at high ISO is not generally applied to raw data (though that is changing with some cameras). I think there are many, many photographers who would say that the D800 also produces pro results, of a different type. The goals of the OP ("mainly portaits and landscape") align more with the D800 than the D4s, I think.
I would think you would be hard pressed to tell the difference between the images the D4s, the D800, and the D750 produce. It is more about camera features that meet your needs.