Ben - Sounds like if you occasionally entertain 20 people, you should get a #2.
I have a #1. It's perfect for me. I don't even lust over a #2. But I only smoke for 2-3 people, 6-8 rarely. I love the way I can roll it behind a chair in the corner of my porch, put the cover on it, a plant on top, and you can't even see it. It's the size of a small end table. That's a plus for me. Although you could easily make enough brisket for 20 people on a #1, you would not be able to feed that many people with some of the other meats, because of the way different meats use space.
The #1 has 3 racks/shelves. I just did a 14.5 lb whole packer brisket. Whole briskets are long, so I cut it into 2 pieces (separating the point and the flat). Put each 7 lb piece on a shelf. The third shelf was empty. In theory you could put another 7 lb hunk of brisket on the third shelf, and that would come to 21+ lbs of meat total. I think I actually could get 8-9 lb hunks of brisket on each shelf, because of the shape of brisket. So it is true that it will hold 21 or so pounds of "certain" meats, but it depends on the shape of the meat. The shelf spacing creates limits for some things. Many things need to be placed on the middle shelf so there is enough height, leaving the bottom shelf empty. Here are some guidelines on what I can fit in my #1.
14-16 lb whole packer brisket, cut in two pieces (leaves bottom shelf empty).
One 14 lb turkey.
Three spatchcocked chickens (butterflied/flattened).
Two 3-4 lb whole chickens (leaves bottom shelf empty).
One 8-10 lb whole chicken (leaves bottom shelf empty).
One 8-12 lb pork butt (leaves bottom shelf empty).
Three full racks Baby Back ribs (cut in half, so 6 half-racks).
Two full racks Spare ribs (trimmed so 2/3 rack on two shelves, and remaining 1/3 rack pieces on the third shelf).
The originator of this thread seems long gone, but maybe this info will be helpful to someone else browsing the forum.