[3.5] What do you think of Mystic Theurge?

[Optimystik]

That is better than most wizard 20 builds, just due to the added versatility combos.

He said Cleric, not Archivist.

To benefit from those 13 levels of Cleric, you need at least 16 Wis to gain access to the 6th-level spells... then you need at least 19 Int for your Wizard side.

This necessitates either high point-buy, good stat rolls, or good gear... all of which a single-class Wizard could put to better use.