I dont remember ever hearing about or seeing any human make thousands, if not millions of calculations per second.
Really, in what you have said you have shown the power of the brain...
How many calculations do you think it takes to decypter and process the image(s) your eyes see? How many calculations do you think it takes to coordiate movement of a limb? How many calculations do you think it takes to decypher sound?
Now do them all together (without conciously thinking about it) and thats a huge amount of power.
It begs the question, whats the hardware conceptual difference between a brain and a computer.... apart from the brain being organic and at the moment more powerful I doubt a huge amount