That turn bet looks weak. To me it screams "I like my hand, but I'm worried that you have a 6. If you want the pot, rep and it's yours."

If he's good enough to pick up on this is another story. That's where his previous play comes into it for me.

I could see his play as being a set. I could also see it as he thinks you missed the flop, so he's playing aggressive just for that reason. If this is the case, he could have AK or really any hand. I think I like raising more on the turn, but that may tie you to the pot. One thing I'm fairly sure of: he doesn't have 6x.