May I encourage you to increase the percentage by 5-10%?
Yes playing on higher difficulties is not "supported", but on higher difficulties, 5% of that 100 DMG maxed out sniper/Magnum is still only 5 damage more. (200% crit sneak its still only 10-15 extra dmg)
A sneak attack only works once it is not a continuous damage multiplier. One shot only. So while You might be able to gain 200% through perks and crit and whatever (I don't know exactly what the perks do), 5% is useless. You do not feel 5% if zombies have 600+ health.
I can't tell if its balanced yet obviously. But just from experience I think 5% is so little that its useless.
Also 200% knifedamage... when the machete already deals about double damage is weird...

but allright