Play the nuts fast?

[Rococo]

HU NLH 1-2.

I have approximately $160 and my opponent has approximately $140. My opponent is not strong. He makes the usual HU mistakes. He is weak tight if he misses the flop. I have been relatively passive pre-flop but I have been pushing him off a lot of hands on the flop with pot sized bets. On the other hand, he hangs on too tight if he catches top pair on the flop.

My opponent is on the button. I am in the BB with 4 [img]/images/graemlins/spade.gif[/img]4 [img]/images/graemlins/heart.gif[/img]. He limps and I check.

Flop comes 4 [img]/images/graemlins/club.gif[/img] 4 [img]/images/graemlins/diamond.gif[/img] k [img]/images/graemlins/heart.gif[/img]. I bet $4. My opponent calls.

Turn

6 [img]/images/graemlins/club.gif[/img] -- I check. My opponent bets $10. I push. He calls.

My line obviously worked here, but I am curious as to whether others would have waited until the river to spring the trap. Also, is there any hand that my opponent could have held that would have justified calling my raise? If not, does that mean that I should have tried to bleed him rather than impale him? What about checking the flop? I obviously knew that I was taking a risk that my opponent folds on the flop, but is it worth it? After all, if I check raise the flop or the turn, it is going to smell a hell of a lot like a set of fours and he may shut down.