While this is certainly a very good chart, comparisons with the Canon's 800mm will be inevitable.
FWIW, Canon prepares its MTF charts differently - the way to read a Canon chart is explained below.
Now take a look at the 600mm II's MTF chart ... looks very good. The Nikon's 600mm's MTF chart is also attached for comparison.
Canon's 800mm needs an update but I'm sure they'll catch up.