There are many threads on this but I haven't found anything conclusive. I'm not using shadow warrior. Let's assume I have 100 in sneak, the first 20% stealth perk and I'm using a muffle enchantment. I'm not sure if fortifying more is all that useful as I'm not really sure how increasing sneak affects things like line of sight, lighting and the sound of spell casts.
You can make glitched fortify sneak enchanted equipment. Which provides wacky bonuses like fortify sneak 10000%. It practically leaves you impossible to detect. Just keep hitting the enemy in sneak mode, and they will never find you. If you're familiar with the fortify restoration potion glitch, then you know what I'm talking about.