Anecdata and not what you're asking but relevant.
I saw a talk by David Battisti (Univ Washington professor). He had attended a FAO meeting about climate change and agriculture.
It looks like it is increasingly hard to engineer wheat/rice varieties that can reach peak yield with rising temperatures. The outlook for say, Indian river production, is not good at all.
From what I remember, we are currently in the temperature sweet spot for rice/wheat production.
If someone knows a primary source for this kind of thing, please comment