I suspect it has to be an autobrake setting as maximum manual braking would be a variable. Airbus did some tests on the A340 to check maximum manual braking against max auto brake and the auto brake won every time. Reason was primarily that pilots could not consistently keep maximum brake applied throughout the deceleration. Although Boeing do say max manual is going to stop you in a shorter distance (so it is different to Airbus in this respect) I am not sure they would put something which is variable as the landing performance datum.