The stamina cost of your power attacks (as is always the case regardless of wield-style or weapon-type) is based on the weight of the weapon you are using. Therefore, in the interest of increasing damage, you'll want the highest base damage weapon combination possible. The damage (when attacking with both weapons simulataneously as with the dual-wielding normal attack-pressing both right and left attack-or the dual-wielding power attack-pressing and holding both left and right attack) is based on the damage of both weapons. This is why it is recommended to equip a dagger in the off-hand they are the lightest one-handed weapons in the game and therefore impart the highest attack speed/lowest penalty to attack speed.
The speed of your attacks, for example, is based on the weight of the weapon in your off-hand (left).
Dual-wielding is not as simple as equipping weapons in both hands simultaneously.
