There are three gishes that don't use divine power:
1) Paladin 2/ Sorcerer 4/ Spellsword 1/ Abjurant Champion 5/ Sacred Exorcist 8
2) Fighter (or any other full bab class with the profs, but really the bonus feat is sexy) 1/ Wizard 6/ SS 1/ Abjurant Champion 5/ Eldritch Knight 7
2a) Replace fighter with LT barbarian. Costs more feats, but is acceptable if you can't get pounce by any other means (such as polymorph, druid wands, dorjes).
3) Wizard 6/ Swiftblade 10/ Abjurant Champion OR Unseen Seer 4
Anything else is pretty much inferior to these in play at any level in any game.
So yeah, the only case where spellsword costs feats is where you are GETTING POUNCE. Pretty snazzy deal, actually.
Final note: Yes, you can trick your way into gish classes with otherworldly and similar tricks, but those cost feats too!
Really swiftblades are down at least 4 casting levels and do fine, but the more caster levels you give up, the more power you give up.
That's because incredible actions and (Ex) defenses are incredibly good
. If the miss chance wasn't (Ex) (making it nonmagical and thus not negated by true seeing or AMF grapplers) then swiftblade wouldn't pay off until level ninth level or character level 15
. That's high enough level that it may never see payoff
. As is, until those levels it barely is worth the CL loss, but is worth it
Yes, swiftblade is INCREDIBLY sexy. Bonuses to saves, a piddly minus two to saves (if you're in melee with them already at which point saves don't matter), and first level maneuvers is not
So yeah, swiftblade is worth 4 CLs because the class features are INSANELY good. It's actually my favorite non DP gish period.
edit: The best gish is an incantatrix that just persisted Shapechange and Divine Power
This is pretty much true.