Going along the lines of PA, have you ever looked at the Arcane Duelist? Specifically the Dextrous Attack and False Keenness abilities. Do note they have a typo in False Keenness where the damage should be reduced by 8, not 12.
I did a brief write-up on this class at one point, though I forget if I posted it.
Dexterous attack has no restriction preventing you from using it with a two-handed melee weapon, so with dexterous attack and Power Attack, a literal reading of the rules allows you to use dexterous attack to convert damage from your weapon damage die or dice to attack bonus and then Power Attack to convert attack bonus into damage. This results in a very favorable conversion ratio because each 1 point of potential damage on a weapon die is only worth .5 expected damage while you get to convert potential damage one-to-one into attack bonus and then two-to-one back into actual damage with Power Attack for a net ratio of 4 damage for every 1 damage on your weapon's damage dice once your BAB is high enough, or 1.5 damage/BAB assuming your weapon's dice are larger than your BAB. However, you lose damage from your non-dice damage bonus first and the conversion ratio on that is only two-to-one or 1 damage/BAB. This means that dexterous attack pays off the most with whatever two-handed weapon has the highest die size and with the lowest possible non-dice damage bonus, so with low Str, weapon enhancement bonus, and fixed damage bonuses from feats and class features. Weapons with two or more damage dice are also disadvantaged. If your immediate thought is that the way to optimize dexterous attack is with a spiked chain (despite its two dice), Weapon Finesse, and sneak attack, skirmish, Arcane Strike (CW 96), or Dragonfire Inspiration (DrM 17-18), you'd be right. There are also some non-core finesseable two-handed weapons, or one-handed finessseable weapons that can be used in two hands, that would work; I'm sure Captnq's weapon handbook has a list. On the whole, the numbers aren't spectacular for an investment of two feats (Dodge, Mobility) and three to four class levels (three levels for the ability, one for the ability to cast 1st-level arcane spells), but it might useful for some niche builds.
As for false keenness, the long and short of it is that it and dexterous attack don't work well together. A weapon with the minimum possible critical multiplier, 2, does 2 damage/point of fixed damage bonus on a critical. If we assume that the 12 is a typo, converting that same point with dexterous attack does 2 damage via Power Attack, but you lose 2 damage from the interaction so your critical does the same damage as if you didn't have or use dexterous attack. If your weapon has a higher critical multiplier, your criticals lose damage relative to not using dexterous attack. You can make dexterous attack net positive with false keenness if you have increased Power Attack multipliers or little fixed damage bonus, but this is a lot of work for little reward. Beyond that, optimizing false keenness's damage requires you to do the exact opposite of optimizing dexterous attack's damage, because to maximize damage from criticals, you need to maximize your fixed damage bonus, but to maximize damage from dexterous attack, you need to minimize your fixed damage bonus. There's probably some way to thread the needle by finding an appropriate non-core weapon that's one- or two-handed, finesseable, and has a 19-20 or 18-20 threat range and getting things that add extra dice on criticals, but criticals are not good for lots of reasons entirely independent of false keenness's problems, and false keenness still gives a penalty to your attack bonus that you could instead use for Power Attack to get more damage on all your attacks. Basically, it's not good.