Am I overthinking the hand?

[gutshot1]

I was in a live 5/5 no limit game when I picked up pocket kings. I raised preflop to 40 and got 3 callers. The flop came:
K [img]/images/graemlins/spade.gif[/img]
10 [img]/images/graemlins/heart.gif[/img]
3 [img]/images/graemlins/club.gif[/img]

First guy checked I bet 60 button raised to $140. He is a sneaky player that knows I am a solid tight player. The small blind folds I just call. Turn is a 9 [img]/images/graemlins/diamond.gif[/img]. I check he bets 300. My original read was that he had pocket 10s but it quickly changed to maybe he has QJ which makes the straight. I just call hoping the board pairs. River is a 2 [img]/images/graemlins/club.gif[/img]. I check he thinks and goes all in for 615. I had 915 total. I thought for 3 mins and folded my set of kings.

I had made up my mind that if the board did not pair and he went all in he had to have had the straight. Would you guys have folded this hand?