KK: Hero has no clue

[BoxTree]

Commerce, 9-handed, 400 NL, 5/10 Blinds

Relevant stacks/reads:

Hero: $1,300
Villain: $1,800, has been playing slightly loose and pretty reasonable postflop. Has not been caught bluffing and I don't suspect he has bluffed in any large pots.

Hero is UTG+1 with K[img]/images/graemlins/heart.gif[/img]K[img]/images/graemlins/diamond.gif[/img]

UTG folds, Hero makes it 40, 6 of 7 call. If you don't believe me, ask Private Joker.

Flop (7 players, $280): 5[img]/images/graemlins/club.gif[/img]4[img]/images/graemlins/club.gif[/img]5[img]/images/graemlins/diamond.gif[/img]

Hero bets $300, Some folds, Villain (MP) calls $300, Some more folds.

Turn (HU, $880): 9[img]/images/graemlins/heart.gif[/img]

Hero...?

Villain likely has:

a) a five
b) a medium pocket pair and thinks I have AK
c) a flush/straight draw with two overs (on the flop)
d) absolute nonsense

If he were last to act on the flop, I wouldn't be so sure that he has a five. The fact that he smooth-called the flop with players left to act behind him makes a five more likely. Would he really smooth call here with a draw or PP when there are other players left to act? If anyone behind him has a five, that player will now almost certainly push (much of the table had deep stacks, so a push wouldn't be small potatoes), and now Villain has to fold his PP or pay a filthy price for his draw.

So, what do I do?

And is my flop bet okay?