Some gem efficiency sheet

Hi!
So I was wondering if there is any sheet that would show some gem efficiency for individual characters. Since full 8 is not effective for any character, then if there is a table, or at least a rule, when it is simply not effective to improve a given dmg or cd gem.

I know that something like this existed before, but it is no longer relevant, because the characters, their skills and dmg distribution on individual skills have changed.

On all my characters I have lvl 8 gems on the main dmg skills (about 60-80% - I have more of the same characters, so it is not that unrealistic). And I am faced with a dilemma of what to improve next.

I know on lost ark nexus is gem priority for all classes but It does not tell me - hey, this is efficiency on lvl 7 and 8 is not worth or level 8 is worth on this skill.