I found a nice script somewhere around, that ouputs the exact chance a lvl73 boss will have to crit you, reducing talents included. Just copy&paste into your ingame chat. The paperdoll rounds up, this script not.
/script DEFAULT_CHAT_FRAME:AddMessage(2.6-(GetCombatRatingBonus(CR_DEFENSE_SKILL)*.04+GetCombatRatingBonus(CR_CRIT_TAKEN_MELEE)),1,0.5,0)