Our current cpu's are on the nanometer level, while our brain is made on the micrometer level which is 1000x larger than that of the cpu. Scientists have made their first organic cpu by using rat brain cells that formed 50,000 to 100,000 neurons and controlled a remote control vehicle. The diffrence between transistors and neurons are rather small when compared to what they do. If you were to take the most advanced cells, human brain cells in a dish that had pins like that of a cpu socket in a computer. Then you trained them, by giving it input and then giving it the result it should come to then. Eventually taking away the results so that is could reproduce the correct results itself. I imagine the neurons that were created as a result of this intereaction would be far more efficent than current cpu specs.
A normal human brain has 1000 trillion neurons. Imagine a organic cpu that had 1000 trillion neurons/transistors and was thinking and consistantly improving itself by repetition. The processing power of such a organic cpu would be unbelievably powerful. If you were to convert the brains 1000 trillion neurons into transistors, you would have a cpu that had one million three hundred nineteen thousand times more transistors than a AMD 955 BE.