Military Performance grade is, in general, many of those things that don't get an academic course letter grade. In-company performance in military duties and attitude.
USNAINST 1531.51 series, as I recall, discussed the various grades and how academic order of merit and overall order of merit were calculated. There will be some discussion there of various grading areas.
I am not current on whether conduct demerits/conduct grades are scooped up in the military performance grade as calculated under present policy. No doubt a current mid or recent grad will know.
Supe's List (occasionally known for the "Nerd Star" pin) is a composite, excellent grades, excellent scores all other areas, no major misconduct.