You can easily smoke 4 slabs of St. Louis trimmed spares or 6 slabs of babybacks on the BGE/Kamado Joe using the Adjustable Rig with oval cooking grids. (Ceramic grill store). With the "Slide Guide" option, you can remove the top and middle grid without removing the entire adjustable rig. (Which is easy to do) You can actually cook on 3 levels if you use the "Spider" and 13" pizza stone as a heat deflector but you might singe the ends of the slab as the stone wouldn't protect them. (You can cover the tips with foil, though).
The offset style cooker is the least efficient style of cooker... and requires the most attention... fun if you have the time and like fire tending. Kamados (including the Broil King Keg) are the most efficient and the vertical smokers are somewhere in the middle. An insulated vertical smoker can be nearly as efficient as a Kamado.