I'm not sure about any records, but try using Viconia, just for the fun of it. She already has high MR of herself. Try equipping her with all the things you mentioned and then make her cast a few Armours of Faith.
Let uys know how high she gets OK? Also, wizard slayer kits gain magic resistance as do monks, so you'd have a headstart with those as well.
I do remember my Korgan being completely immune to fire, must indeed have been around 125%. He could stand right in the middle of a fireball and not scorch a single hair of his beard!
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Melusine, Archbabe of the OHF and the LH
Your voice is ambrosia