improves things slightly further (slight inconsistencies with the above
are because my laptop's currently on battery power):

  canada.json
  old (1.450930341 96 0.7616264250000002)
  new (1.161926076 32 0.24752529000000045)

  citm_catalog.json
  old (0.686048204 68 0.5394565070000006)
  new (0.267222201  6 0.048179708000000154)

  twitter.json
  old (0.362725099 40 0.2935560630000005)
  new (0.099399607  2 0.01469844000000009)

And yes, I have added a test case for this locally.

-- 
Basil