Read this interesting article whilst reviewing my ranges.
When facing a 3-bet OOP you really have only two choices folding or 4-betting. Defending by flatting and playing fit or fold poker you are going to be setting money alight and it is difficult to steal or outplay your opponent when OOP. 4-Bet size should be in 25-30BB range where pot would be 37.5 BB given 100BB stacks. This puts our opponent in a shove-or-fold situation. By betting a bit less than pot his 3-bet bluffs still fold and his 5-bets still shove so we save money on our 4-bet bluffs when he goes all in.