Assuming the CO opens with maybe top 15-20%, and you three-bet with maybe top 10% (although I think a three-betting range is going to be tighter), most of the time I think it's an easy check-call by the CO on the turn with this board.

Edit: Wow, this was a weak analysis. Probably not such an easy check-call. Pot size is 5.75BB assuming you bet the turn, and the CO will fold the river with less than TP, but will possibly collect one BB when he makes two pair or better (as you'll fold to a CR when making a value-bet/check behind sometimes).

As such, anything with six outs or better shouldn't fold the turn, and given the board, a lot of hands will have at least a six-out draw or already be made. But the CO has to consider that the outs may be dirty, and may fold the turn when a call would correct. I don't think the smaller pocket pairs are peeling the flop after the three-bet, so that leaves drawing hands/hands with showdown value which will probably continue.