I have been cooking with a 6 quart roaster for about 4 years, and just cooked 2 chickens in the large roaster. If I were you, I would purchase one, and practice cooking on one before you have to cook for 30+ people. It cooks differently than an oven.....
http://www.amazon.com/Nesco-4816-25P...+nesco+roaster
Just my honest opinion.