I cooked 24# of brisket (two 12# flats) in my #2 recently. Set the auber to 225 & to reduce heat to 140 upon reaching an IT of 195. Expecting a continued rise of 5 to 8 more degrees since the heat isnt bled off by opening doors. I checked the box 15 hours later & the cooldown was well on its way. Box temp 140 & IT 165 & dropping. I dont really find an increase in time is required for larger meat loads although I understand the concern. Still between 1 to 1.25 hours per pound for brined & injected bruskets. Briskets were absolutely perfect. One was used for a Santa on the Bayou party where he arrives by boat with a lighted entourage and fed brisket sandwiches with chipolte aioli & pickled onion, serrano & cabbage slaw on fresh baguettes. The other was served in a similar fashion to a cancer infusion center. There were no leftovers & a great deal of compliments. You should have great success, as well. Good luck.
