Imaging Resource has posted their image quality comparison between the Canon EOS-1D X Mark II and cameras such as the original Canon EOS-1D X and Nikon’s latest flagship, the D5.
Canon EOS-1D X Mark II vs Canon EOS-1D X at ISO 1600
The 1DX Mark II continues to resolve fine detail a little better than its predecessor here at ISO 1600. Luma noise appears to be a bit higher in the shadows from the Mark II, but chroma noise is better controlled which may be why the 1DX II doesn’t do as well with our tricky red-leaf swatch (the fabric has probably also faded slightly since the 1DX was shot). Still, overall image quality is similar. See the full comparison
Most sites and reviewers are finding that the new EOS-1D X Mark II does have better image quality than its predecessor, but that the differences are small.