Um... twice Int to damage?

[CryptbornAkryea]

Do these actually stack?

Insightful Strike (Ex): At 3rd level, a swashbuckler becomes able to place her finesse attacks where they deal greater damage. She applies her Intelligence bonus (if any) as a bonus on damage rolls (in addition to any Strength bonus she may have) with any light weapon, as well as any other weapon that can be used with Weapon Finesse, such as a rapier, whip, or spiked chain.

Battle Cunning (Ex): Your instinct for seizing the moment gives you a significant advantage over foes unprepared for your attack. At 7th level, you gain an insight bonus equal to your Intelligence bonus on melee damage rolls against flat-footed or flanked opponents.

[Karnith]

The bonuses are not of the same type and do not come from the same source, so yes, they would stack.

[Biffoniacus_Furiou]

That both use your Int bonus is completely irrelevant. What matters is that multiple bonuses of the same type don't stack, and multiple untyped bonuses from the same source don't stack (http://www.d20srd.org/srd/theBasics.htm). Other than that, they will stack.

For an example of multiple bonuses of the same type, a Masterwork Weapon has a +1 Enhancement bonus to hit, and casting Magic Weapon on it gives it a +1 Enhancement bonus to both the attack and damage rolls. It will only get +1 to hit, because two Enhancement bonuses don't stack.

For an example of untyped bonuses from the same source, look at the Swordsage's AC Bonus ability and the Monk's AC Bonus ability. Both provide an untyped bonus to AC, but both abilities are named 'AC Bonus' so they're counted as being from the same source and they won't stack. As another example, both Paladin of Tyranny and Blackguard have an ability called Aura of Despair, which imposes a -2 penalty to saving throws on nearby enemies. That's an untyped penalty, but multiple instances of it won't stack because it's from the same source.

A Gloura (http://www.wizards.com/default.asp?x=dnd/ex/20031003e) with (Chaos) Monk levels and Ascetic Mage, Arcane Duelist (http://www.wizards.com/default.asp?x=dnd/re/20030224a) levels, Paladin of Slaughter, Blackguard, and Mystic Wanderer will add his Cha bonus to his AC four times (Deflection, Monk untyped, Dodge, and Profane) and to his saving throws three times (Unearthly Grace, Divine Grace, Dark Blessing). What ability score it comes from is irrelevant, all that matters is what types of bonuses they are, or what special ability or effect (source) they came from.

[CryptbornAkryea]

I see. I honestly learn something new everyday day here.

The stacking Int seems a bit expensive for my taste, even in a gestalt build.

I am interested to discover other instances of stacking ability scores now, lol

[Karnith]

I am interested to discover other instances of stacking ability scores now, lol
This thread has you covered (http://www.giantitp.com/forums/showthread.php?125732-3-x-X-stat-to-Y-bonus).

[Pluto!]

This (http://www.giantitp.com/forums/showthread.php?125732-3-x-X-stat-to-Y-bonus) might be pertinent to your interests.

Double or triple-stacking Cha to saves is probably the easiest and most playable ability double-stack, and Dex to damage is also pretty recurrable.

[CryptbornAkryea]

You guys are awesome!

[Doc_Maynot]

Add in one level of factotum to add int to your damage and/or to-hit a number of times per encounter