60 people, assume 2 pounds loss per packer, cook packers, and assume 35% loss of weight through cook. I would want 1/2 pound of meat per person if there is just one meat, let's assume it is delicious meat, so 1/2 pound.
30 pounds finish product is what you want.
14 pound packer is what I would shoot for, 12 pounds after trim. Assume 7 pounds finished product, you want 30. 4 packers at 14 pounds leaves you a tad shy of 1/2 pound per person. So, I would go for 4 packers, raw, untrimmed weight of 14 to 15 pounds. Get them as even in size and flat thickness as possible. Choice grade if possible.
I would not mess with the smaller briskets, the 14 to 16 pound brisket has a thicker flat and larger point, offers the most even cooking and cooks more evenly.
Whip It Off, Chambers!
"perhaps...but then again...maybe not..."