Why is Sinister Strike more effective with a sword/mace, instead of a dagger, when the DPS is almost the same?
This is because your Sinister Strike damage is not based on the DPS of the weapon, but rather its damage range. This is the case for all special attacks. Since swords and maces of the same DPS of a dagger generally have a much slower speed, their damage range is quite higher. This is also why say, the Barman Shanker, is a better main-hand dagger than daggers which have a DPS 4-5 points higher than it.