PREFLOP: standard, FLOP: Standard. TURN: You must 3 bet this. I know theres a good chance that the small blind has a straight, but he may just have two pair, and the main reason you must 3 bet the turn is to force any gutshot behind you to fold the times your hand still is best. This pot is large, and protecting your hand on the turn is more important than worrying about whether you are ahead or not.