To answer the question, pretty much any wizard/sorceror build you make will be strictly inferior to a single classed character of the same level. They will also tend to be inferior to other multiclassed characters of the same level.
Which is more effective: Wiz 20 or Sor 10/Wiz 10? One is tossing meteor swarms and the other just learned cone of cold. At the high levels, even levelled spellcasting multiclasses are pathetic. The same is true at just about every level except two (a 1/1 sor/wiz is probably better than either a wiz 2 or sor 2). By level 4, a wiz or sor is casting 2nd level spells and has a caster level of 4 (multiple magic missiles). The 2/2 character has more first level spells but that's it. The level 6 sorceror or wizard is far better off than a level 3/3 mutliclass. The level 6 has higher level spells and gets more milage out of them (due to a higher caster level). In fact, except at level 2, the single class character will always have at least as many spells of level x and X-1 as the multiclass has at level x-1. No matter what level you are, an even multiclass is ineffective.
A high/low multiclass is something you can get away with on the other hand. Wiz 1/Sor 19 isn't that much weaker than Sor 20. The wizard level also makes it easier for the sorceror to take Mage of the Arcane Order levels (although it makes those levels less useful as the sorceror can only use wizard slots for spellpool and will thus be limited to 1st level spells). A more practical use of the wizard level would be to take knowledge skills and qualify for a prestige class early. Still, as multi-class combos go, I think that Pal 1/Sor 19 is a far superior option. Pal 1/Sor 10/Sacred Exorcist 9 would be even better. The other problem with an uneven multi-class is that, even if you have lots of low level spells, your caster level is not high enough to make them particularly useful. A sor 6/Wizard 14 has lots of fireball spells available but only his wizard ones do more than 6d6 damage. Not terribly impressive against CR 20+ critters. Similarly, the Wizard 19/Sor 1 may have lots of magic missiles but his sorceror magic missile spells only do 1d4+1. If I were a CR 20 creature, I'd spend an action to grant all of my foes an unlimited ability to cast 1st level magic missiles as a standard action as long as they promised to do that instead of something effective.
So, even or uneven, the sor/wiz multiclass is not a very effective one. It may enjoy some prestige class support that makes it viable in the future but that's not there at the moment.