my rogue is lvl 40 and his critical is only between 400 and 650 with a dagger that has 27-39 stat's

you see it's pretty useless

and i totaly disagree with using 2x sword

have 1 dagger 1 sword or mace (what ever you want)
just get a macro then when you press tab you switch the weapon's so that your sword is in main hand and dagger in the off hand, and switch back to do backstab when you are in party.