Your optimised char wouldn't have a good fort save would he not? So I guess watching out for spells such as disintegrate, wither limb etc may be something to look into...
However if he does have good fort saves then watch out for the Raging Barbarian of the same level who gets his over 50% hit in....I have found that to always sting....especially if a Great Axe is involved and he has Bulls Strength cast on him.
