Posting this as much for general information as to check if I got my own facts straight. So, here are my assumptions:

* Ray of Enfeeblement does not stack with Symbol of Weakness.
* Ray of Enfeeblement does stack with Waves of Exhaustion/Fatigue, Strength Sapping and the Weakening weapon attribute.

* Waves of Exhaustion does not stack with Waves of Fatigue.
* Waves of Exhaustion/Fatigue does stack with Ray of Enfeeblement/Symbol of Stunning, Strength Sapping and the Weakening/Bone Breaking weapon attributes.

* Strength Sapping stacks with everything.

Now, if these assumptions hold true, the highest possible (hypothetical) attribute damage/penalty you can achieve vs named mobs is:

* Strength: -18 (Symbol of Weakness) -6 (Waves of Exhaustion) -6 (Strength Sapping) -10 (Weakening) = 40 vs Orange and Red Named; -22 vs Orange named (as Symbol may or may not work against them). For purposes of auto-crit only 30 (Orange and Red named) and 12 (Purple Named) would count.
* Dexterity: -6 Waves of Exhaustion -6 (Strength Sapping) -10 (Bone Breaking) = -22 vs Orange, Red and Purple named. For purposes of auto-crit only 12 of those would count.

That sound about right or am I missing something?