[Andy B]

I'm assuming that you're not suggesting that Rusty shouldn't raise the river. Say that the other guy will cap with any Six and nothing else. He has one possible Six that beats Rusty, and two that don't. That's 2:1 against. Rusty has a choice between calling the three-bet and making it four bets. The other guy can't re-raise, so Rusty is giving even money on that one bet. Even if the other guy won't cap every time with his rougher Sixes, Rusty's got an edge, right?

And if Rusty blows this pot, he's kinda screwed whether he caps or not.