Also, given that this is the 20/40 game, and people should be paying attention, if you fold fourth then it looks pretty weak tight. In a game where some players will muck around, it gives a message that all you need to take the pot is to reraise and then catch a moderately scary card on fourth. I think, if you include some big three flushes, which are legitimate hands to try and get heads up with, then a call is correct, and then re-evaluate on fifth.