It'd be knife to see knives get some love like sledgehammers did. Heres just a few ideas for some benefits.
Book 1: move backwards 15% faster after making/landing a melee attack.
Book 2: When landing an attack with a bladed weapon, bleed chance is increased by 5%, and damage from bleed is increased by 3%
Book 3: After landing a melee attack, damage is reduced by 5% for 5 seconds.
Book 4: Melee attacks made with bladed weapons are 10% faster and recover 10% quicker.
Book 5: Zombies that are bleeding have movement reduced by a further 10%.
Bookset completion bonus: Quick and Quiet
Walking and crouch movement are increased by 10%. Zombie alert radius when walking and running is reduced by 15%.
If you have better ideas feel free to add them. I've tried to be think of perks that aren't too insane.
Book 1: move backwards 15% faster after making/landing a melee attack.
Book 2: When landing an attack with a bladed weapon, bleed chance is increased by 5%, and damage from bleed is increased by 3%
Book 3: After landing a melee attack, damage is reduced by 5% for 5 seconds.
Book 4: Melee attacks made with bladed weapons are 10% faster and recover 10% quicker.
Book 5: Zombies that are bleeding have movement reduced by a further 10%.
Bookset completion bonus: Quick and Quiet
Walking and crouch movement are increased by 10%. Zombie alert radius when walking and running is reduced by 15%.
If you have better ideas feel free to add them. I've tried to be think of perks that aren't too insane.