Tony Northrup recently has made a video comparison on image quality and dynamic range for recently released Nikon D850 with D810, 5DS R, a7RII, E-M1 Mark II. The Nikon D850 is now already shipping, you can get at Amazon/B&H/Adorama/Wex Photo/Jessops. Also check in stock status of Nikon D850 here.
Here is quick specs comparison for the new announced Nikon D850 (Amazon/B&H/Adorama) and Sony a7RII (Amazon/B&H/Adorama) and Sony a99II (Amazon/B&H/Adorama). The US price for Nikon D850 body is $3,296.95, will be shipping on September 7th, 2017. See also: D850 Vs. 5D Mark IV Vs. D810 and D850 Vs. D750 Vs. D500.