DxOmark published the full Nikon Z7 sensor test:
With the exception of the uppermost sensitivity values, the Nikon Z 7 has a near-identical signal-to-noise ratio to the D850. And although they are both very good, neither can match the Sony A7R III for the majority of the sensitivity range. That said, the values are so close that it’s very unlikely that you’d spot a difference among the images. However, combining the better noise control and dynamic range of the Sony A7R III at higher sensitivity settings could provide an advantage when brightening images post-capture.