Flopped nutstraight on a pairing board vs aggro

[Tropex]

Party Poker 1/2 Hold'em (6 max, 4 handed) pokerhand.org hand converter

Preflop: Hero is BB with 5[img]/images/graemlins/heart.gif[/img], 6[img]/images/graemlins/diamond.gif[/img].
UTG calls, Button calls, SB completes, Hero checks.

Flop: (4 SB) 4[img]/images/graemlins/diamond.gif[/img], 2[img]/images/graemlins/club.gif[/img], 3[img]/images/graemlins/spade.gif[/img] <font color="#0000FF">(4 players)</font>
<font color="#CC3333">SB bets</font>, Hero calls, <font color="#CC3333">UTG raises</font>, Button folds, <font color="#CC3333">SB 3-bets</font>, Hero calls, UTG calls.

Turn: (6.50 BB) 4[img]/images/graemlins/heart.gif[/img] <font color="#0000FF">(3 players)</font>
<font color="#CC3333">SB bets</font>, <font color="#CC3333">Hero raises</font>, UTG calls, <font color="#CC3333">SB 3-bets</font>, <font color="#CC3333">Hero caps</font>, SB calls.

River: (16.50 BB) J[img]/images/graemlins/diamond.gif[/img] <font color="#0000FF">(3 players)</font>
<font color="#CC3333">SB bets</font>, <font color="#CC3333">Hero raises</font>, <font color="#CC3333">SB 3-bets</font>, Hero calls.

Final Pot: 22.50 BB

Should I have capped the river? SB is 46.15/25/2.38 (3.5 on turn) over about 50 hands (not much, i know but he appears to be looseaggro).

After the flop I was thinking 2 pair or A5. I didn't put UTG on anything worth mentioning (65/4.88/0.71).