http://www.project1999.org/forums/sh...ad.php?t=48312
I don't think AC is super effective of course. But lets say 30AC means I take 3% less damage. At 1750 self-buffed HP, that's ~50 hp. At 2800 hp equivalent with rune/bedlam, that's 85HP. So even a pretty small change in damage taken can make a big difference.
Anyway I've never done any testing so I have no real justification for that.