One of the number-crunchers believes the hard cap for mitigation is 32500 Armor/Spell Resistance, at 650 per 1% mitigation. ZOS had also mentioned their mitigation formula is logarithmic, which can mean this hard cap changes with level or the mitigation gains decrease as you go higher in Armor/Spell Resistance. Both of these statements are speculation (the former backed up with a little math), so do not assume these to be true.Are you already over the mitigation cap?