[AthenianStranger]

Well I posted a long reply which was subsequently lost in the void, so to summarize: I think betting the river is better than checking because you are showing aggression all the way, and you may get him to fold a flush draw containing a four or a six. By checking it is very likely that he will push and you will have a more difficult decision. I think a bet of 275 would be good. It's likely he has a missed flush draw with no pair, or even a missed straight draw with 56 and will fold his 6s on the river to what he thinks is an overpair.

Basically I think we've all been in such situations where we've called down with A-high and won, and been sure that we would win. It really depends on the maniac. Some will be passive postflop like this with missed overcards, and aggressive with small pairs. Many will call with missed cards in position when it's clear to them that you've missed, hoping to bluff the river. Many maniacs get like this in big-stack mode. That's why I think betting is better.

We have all bet/called with A-high on the river and lost, too.