This however provides the same stacking saving throw bonus vs Chaos, and to give a broader use to such end game set item (on some builds the ac difference between Forged Chaos and Sparten woudn't even be noticeable) I think you can stack the deck a bit more.
Sparten purpose has always been to protect not-demi druids and low disci dex/uni shield users, and we can safely ignore the formers in PL areas. On the latters I'd rather take my chances on checks(especially with upcoming proposed slag edits) and wear a better shield... at least until it gets destroyed. Instead of acting as a replacement, a anti-slag shield should be something you feel compelled to wear since the start of the filled-with-slag-enemies run, knowing you give up something, not ''everything''.
Armor Bonus +16 (AC Shield Modifier) Bonus Feat: % Anchoring II //this doesn't stack with asmo belt or similar items Skill Bonus: Craft Armor +15 //various stuff based on the ''hold the line™'' concept Skill Bonus: Discipline +15 Skill Bonus: Parry +15 Immunity: Knockdown Damage Immunity: Bludgeoning 5% //looks like all XR large shields have at least this Damage Immunity: Piercing 5% Damage Immunity: Slashing 5%