Spellchuckers: When does their power "top out"?

[Klorox]

Just wondering. I'm thinking about my proposed party, and instead of certain casters going very high as casters only, I'm thinking about mixing in other levels just to give a more sturdy overall character. For instance, if you multiclass in a level of Monk, Cleric, or Bard, you're really helping your saving throws out a lot. Monk adds Evasion, which is great if you don't wear armor, Bard allows you to sing if you can't get into combat right away, and adding a level of Fighter or Ranger can really help out a character to become a much better combatant. A level of Barbarian adds a ton of HP and a Rage, which is nice too.

So, when do Clerics "top out"? What about Wizards? And Sorcerers?

TIA

[Dedigan]

You really won't see much improvement with a cleric after level 15 or 16. 9th level spells aren't anything useful and the higher spell penetration from higher levels of symbol of hopelessness (my favorite HoF spell) don't really help that much, but they do help some.

Sorcerers and wizards do get a little better at higher levels, but adding in about 10 levels of add-in classes can help more, depending on your play style. You won't gain a lot of spells after level 19.