Like Enio said, I can't see a DPS increase using Dead eye. I tried it at level 5 and nothing good to my eyes... The feeling is that my medium speed long bow became a slow speed bow.
The skill have a low mana cost but it does not have a good effect. I'm sure I will never put points in this spell. Right now, is just one more spell to spend mana and do nothing but trade attack speed for damage, and a balanced trade, no DPS increase.
Why this name BTW? I don't get it.
Maybe this isn't a good spell. Some users have great ideas of new spells that can fit better than Dead eye.
You could get rid of this new spell and put a spell like "Double target" where the marksman can fire two arrows, each one on a diffent target that is in a close range to the selected enemy. IMO, this fits more with the name of the tree (Aiming) and is much more usable. Just a crazy idea but who knows?! Think about it
Best regards.