When to (semi)bluff at this pot (sirio is in it)?

[Tyler Durden]

Yet another from the Party Saturday 200k.

Level one, bb is 40. Cutoff opens to 100. I coldcall on the button w/ JT[img]/images/graemlins/spade.gif[/img]. Raiser has 4k and I have 5600. Sirio calls in the SB and the BB calls also.

Flop is 754 two[img]/images/graemlins/spade.gif[/img]. Checked to the pfr and he bets 175 into 400. I call as does Sirio.

Turn is an offsuit Ace. checks to me and i check it through.

River is an offsuit Queen. checked to me again and I bet 550 into 925.

what do you think? anyone bet the turn?