Top two vs unknown and big action

[edge]

Converter is broken. Party 3/6 6-max, 5-handed at the moment. I'm in BB with 1000 behind and K[img]/images/graemlins/spade.gif[/img]7[img]/images/graemlins/diamond.gif[/img]. Folded around to the SB with 600 behind, who is new to the table, and I have no reads at all (less than one orbit so far). SB calls, I knuckle it, off to the flop.

Flop K[img]/images/graemlins/club.gif[/img]5[img]/images/graemlins/spade.gif[/img]7[img]/images/graemlins/club.gif[/img], pot around 12.

SB bets 6, I raise it to 20, he raises to 125.

I can see three ways to play it. Folding is simple enough if I think he has a set. Calling means I'm putting it in on the turn, and it would be best if I think he has a strong K or some two pair. Reraising is good if I think he has a draw, but he may fold a weaker made hand than my top two.

What's your move?