I've played for 2 years and have never had a +5 bursting dwarven axe either...
I would say that I think piercing is superior in DPS in general for a barbarian.
why?
A. Wounding of Puncturing (it is situational but **** is it efficient when it works)
B. Pick crit ranges... for a barbarian dwarven axe has a "crit factor" of 8 and a pick has a crit factor of 12 so about 33% more and I think that will generaly outweigh base damage differences (about 4 points flat). Those are just the plain numbers on those weapons.
For a piercing TWF barbarian I'd go human, you get Oversize as well as STWF that way. The down side is weaker saves and a tad less accuracy.