You can take all of them actually because they all stack. You can have a +8 wisdom modifier at epic level if you take demigod without ruining your build. With that it's +8 dmg on that second attack; with Pit fighter that makes 16; isn't it a bit much however you look at it?
I think it's simply better than any other dmg-bonus feats.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.