How did you decide on "somewhere around 7" concepts in thought at once? What counts as a "concept"? If you are referring to the 1956 George Miller paper "The Magical Number Seven, Plus or Minus Two", then that really has little to do with "concepts".
"That essay reviews psychological experiments that discovered people had a hard time remembering more than about 7 unrelated pieces of really dull data all at once."
See Tufte: http://www.edwardtufte.com/bboard/q-and-a-fetch-msg?msg_id=0...
"That essay reviews psychological experiments that discovered people had a hard time remembering more than about 7 unrelated pieces of really dull data all at once."