The bonus comes from base poisoning, therefore there's no gain from magical clothing.
2) New item for Assassins
A leather assassin hood
Perks:
- Hide your identity for as long as you wear the hood
- Boost your stealth by xx steps to normal count
- Boost your backstab power by xx%
Requirements:
- Craftable only from black dragon hide
- Requires high skills from a tailor to craft it
- Requires base skills of 100 hiding and 100 stealth from the assassins to wear it
- Wearable only on foot
- Cannot wear or equip armor while wearing the hood
Leather armor is best for sneaking, because it's literally made from hide.