J, if it answers your question, I'm only cooking three butts today, and they're on my 22.5", not my 18.5". Slabs of ribs are just as good cut in half so that's not a big deal, but it's nice to be able to smoke several whole slabs without rib racks. Using my extra grate, rib capacity is six full spares, nine st. louies, or a dozen back ribs. Overcooked slab ends is what you get if not cooking half slabs on the 18.5", but like I said, nothing wrong with cooking 'em like that. Anyhow, another thing is that I won't miss squeezing another brisket on my little 18.5".
If I was only cooking two butts today though, they'd be on my 18.5", mainly just to save some fuel. I cook for a crowd so I use the big one most of the time, but both of mine are great cookers. One other thing is that a cooker crammed with meat takes a while to come to temp, and I'm impatient. I wouldn't get rid of my small one, though. Recently I used both at the same time to cook 30 lbs of chicken leg quarters. Only two grates on each cooker were used, and I was able to cook fast enough to get it all done in about two hours without cracking either door.