It is a very rare situation when you want to consider 5-bet bluffing. It does occur, but it’s often as a result of you having pissed off an opponent. That is not to say it is an unprofitable play. Oftentimes the 5-bet is such a small additional amount compared with what’s already been invested that the play seldom needs to work.
No, it’s a rare play because it comes up so infrequently. People do not 4-bet bluff nearly as much as they used to. When they do try to bluff in this manner they tend to select stack sizes which lend themselves to it well.
There will come times where you’ve built up a history with a person or you feel you’ve 3-bet one time too many the second the chips leave your hand. Then it’s possible to think of a 5-bet bluff, especially if the 6-bet by your opponent will force him to move all-in. I determine whether I am going to do this play by looking at the person’s 4-betting combinations. If historically you see a ton of bluffs than it’s very wise to put in a 5-bet here.
Sometimes, you will find players even do different sizings when they’re bluffing. There are a few opponents I can see through NoteCaddy replays who 2.1x raise over my 3-bets when they have a crummy suited connector or ace, but go 2.5x or higher when they have a real hand. Playing these people we should flat many of our good postflop holdings (the suited gappers) and 5-bet with our mediocre big cards, as they are blocking a large percentage of his 6-betting combinations and are likely to go bust on any high-card board.