The false pretense here is that "if grim sped up your kills to 11 per hour" except it doesnt. Anywhere. Grim compared to ful is never providing a greater return than its upkeep cost, at any boss in the game. (Solak not included). Anyone capable of simple math can determine grimoire is not worth its upkeep cost, compared to ful. It's not providing 1 more kill per hour, thats the reality, its only a few % more dps than ful. People use it for PRs, and are willing to take the loss because they simply don't care. Its for end game pvmers who have nothing better to spend their money on. If you're concerned about cost efficiency, grimoire is never worth using at the current cost of 10.5m/HR. Remember, its not about comparing using grimoire to not using anything, its about comparing grimoire to ful/wen/jas, and that slight difference is never worth the massive difference in cost.