Ultimate Magus in gestalt

[ImperatorK]

In a gestalt game where dual-progression/hybrid PrCs are allowed but take both sides of the gestalt, what would be better - Wizard 20 // Sorcerer 20 OR (Wizard 10 // Sorcerer 10) / Ultimate Magus 10? (You can substitute Sorc with Beguiler if it bothers you.)
The Ultimate Magus sacrifices just 1 caster level of Wizard and 2 CLs of Sorcerer, but gains some decent abilities instead and both Wiz and Sorc still reach 9th level spells. IMO it's worth it.

[RobbyPants]

If you create the character at 20th level, it would be totally worth it. You still have 9th level spells plus more goodies on top of it. The only reasons people say not to give up caster levels are either:

1) You gimp your character half the time if you're behind in your top level spells (and this would impact the first 18 levels of playing the character if you started at 1st level), and

2) You want 9th level spells at 20th level.

You don't have to worry about either of those if you stat this up right at 20th level.