The 6bet is one of the most underated moves in deep stacked poker (both cash and tournament). For players who aggressively use the 4bet they will find some players begin to pick up on this. In particular, if you have some kind of a history with a player the 6bet can be a valuable move. Of course, it is also a costly move when it doesn’t work out ;). I have found the play to be highly valuable if you pick your places carefully!