I have a Klose like the one Dave linked. The "cooks for" numbers are not innaccurate but may lead you to an incorrect conclusion. I can pack my cooker with almost 1000 lbs of pork butts. But there isn't enough room for proper air circulation. Some butts will be done in 8 hours, some in 15.
Briskets, chickens and ribs take up more room on the grates per serving, reducing your "feeds" capacity. You're also probably going to be cooking beans and other sides in there.
If you do a lot of ribs you can have extra shelves put in. My pit came with 3 rows in the main plus an extra set of rails and 4 rows in the upright. I have since had a forth set of selves fabricated for the main, increasing capacity by a third. There's plans to add three more shelves to the upright to increase capacity in ther by 75%. If I knew then what I know now I would have asked Dave to build it with the extra shelving in the first place. But I was a butt man and didn't know I would become a ribber.
So here's a real world example: with our new fourth row in the main we were able to cook 36 racks of back ribs, 40 St. louis Spares, 20 rib tips, 40 chickens and 4 full size pans of beans. That pretty much loaded it up, main and upright. There was good circulation and everything came out great.
The "Daddy" in Smoke Daddy's Barbecue