[note: I don't have the new edition and know only secondhand what damages are done there]
This takes into account power attacking, but overcoming DR isn't a simple matter. A guy with a good suit (DR7) and helm (DR2 more) requires the attacking strength 18 dude to have an AP 6 weapon to pierce. Bardiche has an AP of 5 (total of 9 with +4 strength). If the armor isn't pierced, the attacker is dealing 10 fewer points, enough to counter the Power Attack bonus and subtract 2 more from the final damage.
Bardiche attack roll is at -4 and damage is d10+d8+6+8-10: Average 14
Dual open Katar attack is at -10 (big penalty!) and damage is 4d6+4+2: Average 20
So basically, you're at at 30% decreased chance to hit, but a greatly increased chance of dealing massive damage.
They're fairly equivalent. For high BAB characters, the power attack becomes a more attractive option.
Odd rules question though. The book (again, older edition, not latest) says, "subtract a number from all melee attack rolls and add the same number to all melee damage rolls. This number may not exceed your base attack bonus."
It seems that the phrase "This number" is referring to the latter figure of melee damage. Generally, it's not an issue, but for two-handed weapons, the damage is increased to "twice" the number subtracted.
So, does a character with BAB 4 and a two handed weapon get to take a maximum of -2 to hit and +4 to damage, or at most a -4 to hit and +8 to damage?
I'm not curious so much about house rules as I am to see if this was officially clarified somewhere or in the next edition.