At Level 12, a Pact of the Blade Warlock can take the Lifedrinker Eldritch Invocation, which states the following:
When you hit a creature with your pact weapon, the creature takes extra necrotic damage equal to your Charisma modifier (minimum 1).
Assuming a Hexblade Warlock with a 20 in Charisma, this translates to 10 bonus damage per attack. This enormous bonus means that every missed attack results in a significant reduction in damage.
The Sharpshooter and Great Weapon Master feats grant options of the following pattern:
Before you make [an attack] with [a weapon] with which you are proficient, you can choose to take a -5 penalty to the attack roll. If you do so and the attack hits, it deals +10 damage.
At what point is the Warlock's expected damage per attack reduced by using the optional attack modifier of either the Sharpshooter or Great Weapon Master feat?
Assume a Hexblade, Pact of the Blade Warlock with the following characteristics:
- At least 12th level
- Lifedrinker Eldritch Invocation
- 20 in Charisma
- Using a pact weapon, either:
- A longbow
- A greatsword
- ... with the respective weapon feat:
- Great Weapon Master
With the following variables:
- Enemy AC
- Attack roll and damage roll bonuses (due to spells, proficiency bonus, magic weapons, etc.)