The average is 75, if both are same speed. If speed diff is drastic, the faster one will sometimes double-fire between the weaker one's attack. If the worse wand is faster, it increases the loss. Else, it DEcreases the loss. But, you need a wand for alchemist because the wand can be used "from the corner" if its bolt is reflecting. This could be useful for corner-striking bosses or some harder enemies. Generally, only dual to amass effects on two equal-speed, equal-damage weapon. Else use shields, maybe even dual shields.

The average is 75, if both are same speed. If speed difference is drastic, the faster one will sometimes double-fire between the weaker one's attack. If the worse wand is faster, it increases the loss, else, it decreases the loss. However, you need a wand for alchemist because the wand can be used "from the corner" if its bolt is reflecting. 

This could be useful for corner-striking bosses or some harder enemies. Generally, only dual to amass effects on two equal-speed, equal-damage weapon, else use shields, maybe even dual shields.