Decided to compare node/1 between Drupal 7 and Drupal 6. To give some semblance of a level playing field, I put return array(); at the top of menu_contextual_links() since that's our single biggest recent performance regression, and we should have a killswitch / permission for it soon which will do much the same thing. Note the dbs were different, different modules enabled etc., this is just to get an idea
7: 764 different functions called in 335 milliseconds
6: 412 different functions called in 197 milliseconds
I've attached the cachegrind files themselves too, so people can stick them in webgrind / kcachegrind themselves.