This doesn’t actually answer the question; however, in the book Driving Mr. Albert - A Trip Accross the Country with Einstein’s Brain the anatomical detials of Albert Einstein’s brain are discussed.
Apparently his brain was of normal size/volume/weight; however, he had about 10 times as many dendrites as the average Joe. To me this suggestes that the overall size of the brain is rather unimportant - it’s the composition of the brain that really factors when it comes to smarts.
Of course, for this hypothesis to make sense you do have to assume that Einstein was, in fact, smart. I know I’ve had discussions with people who feel he was of totally average intelligence - I don’t agree but have no concrete facts (such as his IQ scores) to bolster my opinion.