[Andy B]

Failing to three-bet on fourth approaches crime-against-humanity territory. Fifth is worth a raise as well. On sixth, you do have enough hand to take all that pressure. There is a certain amount of money in the pot and any low card should be good for half of that plus half of what the second-best high hand puts in on both sixth and seventh streets.

I three-bet the river. The only reason not to do so is if you think that the original bettor might fold for two more bets. While some might bet and fold to a raise in hold'em, it doesn't happen that much in this game. If the guy is afraid of being beaten, he's more likely to check the river.