Are human beings so much smarter than Chimps really?

Humans and chimpanzees shared a common ancestor ∼5-7 million years ago. Their genomes now differ by ~4% (comprising ∼35 million single nucleotide differences and ∼90 Mb of insertions and deletions). That's the difference between the smartest of chimpanzees and dumbest of humans.
That incidentally is within which Beethoven and Bach, or Stephen Hawking and Einstein reside. Or LHC and Hubble Telescope if you like.
It looks like 4% is too little to make so much difference.
This puts us face to face with the following possibilities:
a) Most of human (or Chimpanzee) DNA are junk. That would lessen the denominator in the difference expression making 4% as wrong. May be the difference is not that little.
b) The perception of difference between a chimpanzee and human being (including all of Beethoven, Einstein and Hubble Telescope) as great is possibly flawed. Maybe in evolutionary scale we are just 4% smarter than Chimps.

So which is your best bet? Or do you have a better answer?