My guess is if you can get 5 10 LB pork butts then you should be able to cook all of them on the WSM at the same time. The trick would be to get a 3rd rack and 4 Coke Cans. The dome on the WSM is high enough that if you got a 3rd rack, and used four coke cans filled with sand or water I guess, then you should be able to place to get the third rack to fit in the 22. The coke cans should give you enough height to give you clearance so the warm air can move around the meat uninhibited. So while you want to get as much in there as possible, if the meats are touching each then this would prevent the proper air circulation that you need to ensure a proper, even and timely cook. Heck if you had 4 racks and 8 Coke cans in theory should be able to get atleast 8 pork butts in the WSM with the needed air circulation.
Thoughts?