I always struggle with wether or not I should spread a corp to other civs. I'm thinking that even if we go to war, he/she still gets the benefits of my corp.
Cereal Mills requires less resources for 1, it costs less in maintenance and is less vulnerable from being pillaged.
My calculations for small and standard-sized pangaeas favored Sid's Sushi the majority of the time with regards to food production.
Never played a Great Plains map, but I'd suspect Cereal Mills would finally win there.