Rich,
As others have said, the 10cfm fan works well on the 22.5 wsm. One needs to start with enough lit coals and have the pit probe measuring the air temperature, not air temperature as cooled by the meat.
Getting ready to put on a 16.5 brisket and 2 nice sized butts for a total prepped meat load of approx 34 - 35 lbs.
Followup : Brisket ready at 9 hrs and butts an hour later. Plenty of unused coals left. Only issue was the over sized pecan wood chunks igniting thereby sending the temp over set-point. Caused a few control problems. Lesson learned.