What about total time for multiple cuts?(i.e. 14# brisket and 9# butt) Do you figure 20-28 hours for the brisket and 12-18 for the butt, or do you figure 35-46 hours for both to come off at relatively the same time?
Meat cooks in parrallel, so ya dont add the cooking times together, they stay seperate. Maybe add alttle extra time for a higher load, just due to additional tending, but that additional time goes to the end of each cuts individual estimate.
For angus briskets I go by 1hr to 1:15 per lb. Awagu or Kobe briskets 45 minutes to and hour per lb.
Pork butts 1:15 -1:30 lb and chickens 45 minutes lb.
All these are at 225-250 range.
I think that as long as you have sufficent circulation, the volume of meat doesn't add significantly to the lenght of time it takes to cook it. What does add to it is the increase in time the door is open to tend to more stuff in the chamber, or the additional volume restricting airflow.
Initially, it may take a little more fuel to maintain temps if your using cold meat all at once, but once the meat takes on a heat load it should level off. Key is the circulation. As long as the heat is moving, times should be pretty consistant.