For reference on the TV show on discovery which I think is called, "Human Body Pushing the Limits" they did an episode on the human brain. Showing how the brain works during periods of extreme stress such as firefighters in the middle of a firestorm in a forest.
Their estimate was that the peak of human intelligence could do the equivalent of 3 trillion calculations per second when you consider everything the human brain is doing, (monitoring bodily functions, taking in visual information, analyzing said information, subconscious thought, etc.)
Not sure how accurate that is though.