For what it's worth, here's a mechanic I've considered:
each class has a primary ability; in the case of a spellcaster (wiz, sor, clr, drd), it's caster level.
When multiclassing, you can retain the special ability of your primary class; that is, the class in which you have a majority of levels. Thus, a 12th-level character's primary class, if any, would be the one with 7 levels or more.
This means a Ftr9Wiz11 would have a caster level of 20.
He'd still have only 6th-level spells, the same spells/day as a normal wiz11. Obviously, he wouldn't have gained the wizard bonus feats beyond 11th-level, nor the 2 free spells per level.
Caster level 20 for spell levels 6 and below isn't as big a deal as for levels 7-9; only a few spells (flame arrow, which shouldn't scale to 20, and chain lightning, which should, are two notable spells) even scale beyond 10 or 15.
Caster level is very important, because a wiz11/anything9 can't stand up to the SR of creatures of CR 20 and thereabouts without it. And the wizard's primary balancer, spell level, is still the exclusive province of full wizards.
If you're curious, I don't know what the "primary ability" for most other classes is...fighter is obviously base attack, and that's tricky at best. But that's another story..
each class has a primary ability; in the case of a spellcaster (wiz, sor, clr, drd), it's caster level.
When multiclassing, you can retain the special ability of your primary class; that is, the class in which you have a majority of levels. Thus, a 12th-level character's primary class, if any, would be the one with 7 levels or more.
This means a Ftr9Wiz11 would have a caster level of 20.
He'd still have only 6th-level spells, the same spells/day as a normal wiz11. Obviously, he wouldn't have gained the wizard bonus feats beyond 11th-level, nor the 2 free spells per level.
Caster level 20 for spell levels 6 and below isn't as big a deal as for levels 7-9; only a few spells (flame arrow, which shouldn't scale to 20, and chain lightning, which should, are two notable spells) even scale beyond 10 or 15.
Caster level is very important, because a wiz11/anything9 can't stand up to the SR of creatures of CR 20 and thereabouts without it. And the wizard's primary balancer, spell level, is still the exclusive province of full wizards.
If you're curious, I don't know what the "primary ability" for most other classes is...fighter is obviously base attack, and that's tricky at best. But that's another story..