Efficiency

Level 4 of the Dungeon
(1, -7, D:4)
  a book of Callings

Level 5 of the Dungeon
(0, 0, D:5)
  a +0 hunting sling
(3, 9, D:5)
  a book of Blood
(7, 7, D:5)
  a +0 club

Level 6 of the Dungeon
(0, 0, D:6)
  a book of Spectacle
(6, -9, D:6)
  a book of Air
(11, -4, D:6)
  a +0 ring mail

Level 7 of the Dungeon
(0, 0, D:7)
  a staff of fire {!a}
(0, 1, D:7)
  a hound corpse