100% Invisibility is impossible in Oblivion — the engine hard-caps Chameleon/Invisibility at 80% (80 points).
Result: 80% Chameleon for 60 sec — near-invisible for stealth kills/escape. Recast as needed.
Note: Dark Brotherhood Armor (Ancient Shrouded) has fixed enchantments; you cannot re-enchant it. Craft custom armor/clothing for Chameleon slots.