Agree with @Ed_C , he covered it very welll. But I'm wandering where in the world 6000 cal per day came from? IMO it's not realistic and probably impossible to pack/carry/figure out.
The 1.5-2lbs per day is a very good rule-of-thumb. FYI hiking above 10,000, one tends to not to have a good appetite anyway, for what it's worth.
REI member since 1979!