I did some more testing. They were performed with a testing char with:
100 1h weapons, 70 2h weapons, 5 powerstrike, 15 agi and 18 str.
I equipped both a heavy fighting axe (28c) and a balanced bastard sword (31c), against a full mob of 20+ mountain bandits that wear all +5/+8 armors on all locations, as they're the more uniform foes I can test on with large numbers without risking being killed 10394530 times.
I will call BS1 the bastard sword wielded 1handed, FA the fighting axe (wich is 1handed), and BS2 the bastard wielded 2handed.
Here are the results:
-BS1 and FA speed seemed almost identycal, while BS1 has a slightly more range.
-BS1 and FA damage seemed identycal, ranging from 20 to 30 (they can both score 45+ hits on head or naked feet but that's rare).
-BS1 and BS2 speed didn't changed at all.
-BS1 damage (oddly) seems -higher- than BS2 damage (just a couple of hits tough, no more than 5), but this seemed to be related to the fact I've less 2h skill than 1h (70 vs 100). When I cheated my skill to equal values, there seems to be no more difference.
Conclusion are:
That 31 damage is somewhat a fake or it was intended for 2h wielding, but as the weapon isn't fully implemented (or does not work), there seems to be no difference when using it one or two-handed (except for the skill used).