But just how large is the difference in "to hit" chance, and potentially amount of dmg or crit chance, between 18 and 20 in CHA?
On average, D&D assumes a 65% chance to hit. This stays constant as you level up, because enemy AC
roughly increases with your attack bonus. With a 20 Cha, you're ahead of the curve and thus will have a 70% to hit (A d20 has 20 sides -> you have a 1/20 = 0.05 = 5% chance to roll each value).
If you roll normally, your 20 Cha character, compared to an 18 Cha character, will hit 70/65=1.08 =
8% more often.If you roll with advantage, the formula for chance-to-hit is 1-(1-0.70)^2. 100% minus the chance you'll miss with both rolls, and the chance that you'll miss twice is (1 minus your chance to hit with one roll)^2. Correspondingly, a 20 Cha character hits [1-(1-0.70)^2] divided by [1-(1-0.65)^2] = 1.04 =
4% more often.This also applies to your saving throw spells, although I think the average success rate is a bit less than 65%, so it might be closer to the below...?
This also applies to any Charisma skill checks, although a bit better since many of your persuasion checks won't have Proficiency. At level 5, your 20 Cha Sorcerer will have a 70% success with Proficient skills, but only a 55% chance of success with non-proficient skills.
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Rolling normally, your 20 Cha character will succeed on non-proficient skill checks 55/50=1.1 = 10% more often-
Rolling with Advantage, your 20 Cha character will succeed [1-(1-0.55)^2] divided by [1-(1-0.5)^2] = 1.06 =
6% more often.Overall, your 20 Cha character will be about ~7-8% more effective.Same question applies to the deep gnome wizard I've just rolled. I'll be able to gain 20 in int by lvl 4, adding in Ethels scalp. That should give me an extra spell, which - unlike with the high half-elf sorc - seems like a much clearer advantage, than maybe a slight % added hit chance... right? No?
Eh. Prepared spells are much more important in tabletop, where you have to wait until night to prepare different spells. In BG3, you can re-prepare spells (and long rest) whenever, so as long as you're out of combat you can just prepare it. At level 4+, you're getting to the point where you probably don't
need any more prepared combat spells.
There are too many feats to analyze in detail. If you have a specific feat you're wondering about, I could maybe comment.
Hope this helps!
