
Friendly reminder on armor caps.
Technically you'd need even more without any armor, but without some serious exploitation I doubt you'd get that high, even with Carius' armor (considered robes), amulet of articulation, diadem of the savant, and mage armor.
Edit: Looks like most enemies never get the third rank of the perks, so 1,134 (1,134 - 50% = 567) armor would be enough for pretty much every situation. You'd also still have 283-284 armor rating (no shield) if you did run across an enemy with three ranks in bone breaker/skull crusher.