Yea I always use two handed swords whenever possible. To wield it two handed you just have to drop or put your shield in your backpack and yer guy will automatically 'multigrasp' the weapon. The game automatically places things you pick up in your off hand so you have the slight annoyance of having to do the extra step of putting the item in your backpack after you pick it up. But if yer picking up alot of stuff, like looting a cave or something you only need to do it for the first item.
As for whether wielding a weapon 2 handed is more effective I remember in the damage formula in 40d you only did something like half damage after all the calculations were done, if you were using a two handed weapon in one hand. And I had experienced it myself even before the damage calculation was released. But the damage calcs have most certainly changed now, so I'm gunna do some arena testing. Be back with the results
Test1: Human(Controlled) vs Elephant(AI). While holding a shield the parts were severed 2/3 times (last being the head) However the one time that a part was not severed the attack only 'dented the muscle'. But that wasn't a very big amount for testing, I want more.
Test2: Went badly because the elephant was fully decked out in armor because of my own stupidity. Wielding the sword two handed or I handed showed no difference, nothing could penetrate the armor.
Test3: Also went badly. The elephant kicked my guy in the head the moment he got in range jamming the skull through my brain killing me. The game isn't caring much for science it seems.
Test4: Finally gets some results. dent muscle, briuse bone, briuse muscle, tear muscle, shatter bone, shatter bone, shatter bone, tear muscle, tear muscle, tear muscleandbriuselung, shatter bone when wielding the weapon 1 handed. And....ah crap...
After all that it seems you can't multigrasp a weapon in the arena. Perhaps using the method of getting it stuck in and then grabbing it with both hands while it's stuck in would work, but the critter would probably hurt me too much or I hurt it too much while trying to get the weapon in both hands. Well fudge.
Did the method outlined above and I got the weapon without dying or hurting the victim too much. But it appears to be bugged. I am now dual wielding two two handed swords. I appear to have duplicated it.
I give up, I can't get anything to happen consistently, now with another subject he seems happy to multigrasp his sword. But since this is a diffrent guy his attributes could throw the results off.