In my previous game I had quite big armor, 80+ and it helped a lot to survive the game on hard, so I've decided that on my insane run I would try to make the best armor possible and become invincible.
Well, I've got up to 179 armor with 720 hp, my DR exceeds (almost) all kind of meele damage, but they still do some so "called" minimal damage regardless of my armor and while i haven't died (yet) it actually wouldn't be hard at all. Every damage I take makes me staggered if they surround me they could chop down my hp still pretty fast. A bit dissapointing..

About the build: all points in sword/alchemy, all avaible mutagen slot filled with strength/greater strength + 1 madness mutagen.
In the end i was missing two skill points: I could had used those to get one more mutagen slot for +4 base dr, and +10% dr when poisoned, but unfortunately tthe maximum is 34 points and I rather had the skill which negates the backstab dmg bonus on me.
Before killing the operator guy I used Vigra/rook/swallow+whetstone and my final stats were:
720 hp, 179 armor, 88-100 dmg (from the silver sword for the gargoyle quest), 55% dr from magic etc. still almost managed to die at the second pair of gargoyles :)