Percent damage reduction and more life should be the next thing you upgrade if you want more defensive stats, because 300k defense should be ok. Truce RW belt and Erawan RW armor are good items for damage reduction and Nephilim boots give a good vitality bonus, just make sure to make the best possible base item you can before you put the runes in. Meaning make sure it's superior with 40% or higher defense and gets the oil of luck upgrade, then put enhanced defense MO's or whatever you'd need (10 max MO's)
Edit: then again if you're relying on paragon, runewords drastically lower how many gems you can have. Mix it up, see what works, but of course don't go full runewords if you're using paragon.