With full turning progression, you need 28 charisma to turn enemies at your level 100% of the time. Very few enemies go beyond HD30, the ones that do are:
Crypt Keeper (34)
Valgoth (34)
Netherese Arcane Ghost (33)
Netherese Avenger Ghost (35) <- nearly impossible to turn
Gargantuan Nightwalker (40) <- impossible to turn
Greater Nightwalker (35) <- nearly impossible to turn
Huge Nightwalker (31)
Alhoon Lich (32)
Dracolich (50) <- impossible to turn
Demilich (41) <- impossible to turn
Necrolord (41) <- impossible to turn
So 28 charisma to turn every other enemy but these (100% of the time that is, there is still a chance to turn things at level 34 or lower). Remember that's the final score.
Eagle's splendour provides +4 charisma
Improved Turning feat is like getting +6 charisma
Master of Energy is like getting +8 charisma
Sun domain is like getting +2D4 charisma
So as you can see, you can quickly get most of the charisma you need to turn enemies at your level (so level 30 enemies and below) without having much charisma to begin with. Base charisma is mostly needed to get more uses of turn undead, which is sometimes needed unless you've extra turning feat(s).
But 28 charisma is turning at your level. If you want to turn these others 100% of the time, you need:
To turn level 31 you need 34 charisma
To turn level 32 you need 40 charisma
To turn level 33 you need 46 charisma
to turn level 34 you need 52 charisma
So...even with all the bonuses from above, it's probably not worth it going too heavy on charisma.
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QC has recommended that planar turning has its requirements lowered from 25 charisma to 21 charisma. That should help quite a bit, if that change ever comes live. All the outsiders are level 30 or below, so they're far easier to turn
