I haven't calculated how weapon skills scale, but two-handed is a no brainier (and too OP compared to the other weapon skills, if you ask me.) because of the +crit damage on top of the regular damage increase. Damage wise, two handed skill is better than scoundrel by a huge margin, so it's anything but sub-optimal.
Also, investing in elemental skills forces you to use a single element for the benefit. A staff with two handed skill allows you to use any elemental type with equal proficiency. I just haven't been able to justify doing it, because of that.
But the Wits build will have less damage than a full damage stat build. But the point is to have the flexibility. Being able to swap between magic and physical damage types is hugely beneficial, especially when CCs are so finite, yet exceedingly important. Being able to utilize both magic armor and physical armor based CCs has proved very valuable.
Anyways, I'm not saying it's the best build around. But it's fun and flexible, and relies on a stat that most people claim is worthless.
As for double turns, I haven't figured out what causes it, but I usually get 1 or two per fight, and it never happens outside of me having an insanely high Wits character.
