The correlation between gpm and xpm is 0.95. The more gpm, the more xpm, and vice versa. But some values are higher than expected, some are lower. Efficiency is a difference between the value of xpm depending on gpm (blue dots) with respect to the expected value (red line).
Efficiency
Telescope 64.0900
Psychic Headband 42.3608
Timeless Relic 38.0782
Eye Of The Vizier 35.9834
Spell Prism 33.6050
Ascetic'S Cap 29.3290
Ceremonial Robe 28.1800
Stormcrafter 27.9781
Martyr'S Plate 27.4098
Penta-Edged Sword 26.5300
Quickening Charm 24.4909
Havoc Hammer 22.5555
Dandelion Amulet 22.4774
Trickster Cloak 21.7385
Ninja Gear 21.1453
Mind Breaker 21.0368
Seer Stone 19.2514
Book Of Shadows 14.0311
Ogre Seal Totem 12.1588
Trusty Shovel 9.5264
Seeds Of Serenity 7.0620
Philosopher'S Stone 4.0900
Fairy'S Trinket 3.9101
Tumbler'S Toy 3.7112
Faded Broach 2.0229
Defiant Shell 1.6840
Enchanted Quiver -0.4809
Gossamer Cape -1.2745
Paladin Sword -1.9629
Book Of The Dead -3.4682
Stygian Desolator -4.4543
Bullwhip -4.8174
Arcane Ring -4.8413
Cloak Of Flames -5.1226
Titan Sliver -5.2643
Elven Tunic -5.4227
Arcanist'S Armor -5.9890
Fallen Sky -7.0178
Ex Machina -9.0968
Apex -9.6543
Mirror Shield -12.1864
Giant'S Ring -14.0650
Force Boots -14.5540
Pirate Hat -14.5831
Lance Of Pursuit -16.0175
Pupil'S Gift -28.7019
Grove Bow -31.1767
Vampire Fangs -31.1792
Pig Pole -32.4895
Occult Bracelet -34.9134
Dragon Scale -37.4803
Vambrace -39.9918
Spark Of Courage -42.8477
Duelist Gloves -47.4838
Ring Of Aquila -48.1103
Broom Handle -49.7889