With my quick bit of testing the bonus Undead Race damage from the Sacred Crown makes that better than the +13 Amistr Beret for MVP like Stefan in Sky Fortress. But for fighting Demon Race mini bosses in Sky Fortress I was getting a decent amount more damage from the Amistr Beret.
I tested these:
+13 Sacred Crown
+13 Amistr Beret
with this:
+14 Holy Stick (2x mAtk 2% enchants) True Marg card
Mob Scarf combo
Abyss Dress
+12 Excelion Shield
+9 FAW (Spell enchants)
+7 Shoes of Punishment
2x Magician's Gloves (Headless Mule)
VIP food buff, Clem, and Power of Odin 2
So on Undead Race it was noticeably more damage with Sacred Crown but in most other cases I think I'll be wearing Amistr. Just need to get used to mailing myself b.gems again lol