Wreckless bluff, or smart move?

[young nut]

So I'm fairly new to NL ring, I'm usually a 3/6 limit player. But I have decided to try out some NL. I was wondering about this bluff on the river, please take a look at the hand.

Party Poker No-Limit Hold'em, $ Hero (10 handed) converter

SB ($124.1)
Hero ($110.85)
UTG ($141.15)
UTG+1 ($100.35)
UTG+2 ($100.15)
MP1 ($113.15)
MP2 ($16.3)
MP3 ($192.31)
CO ($50.9)
Button ($27.4)

Preflop: Hero is BB with Q[img]/images/graemlins/heart.gif[/img], K[img]/images/graemlins/heart.gif[/img]. SB posts a blind of $0.5.
<font color="#CC3333">UTG raises to $4</font>, <font color="#666666">4 folds</font>, MP3 calls $4, CO calls $4, Button calls $4, <font color="#666666">1 fold</font>, Hero calls $3.

Flop: ($20.50) 3[img]/images/graemlins/heart.gif[/img], 3[img]/images/graemlins/spade.gif[/img], 8[img]/images/graemlins/heart.gif[/img] <font color="#0000FF">(5 players)</font>
Hero checks, UTG checks, <font color="#CC3333">MP3 bets $10</font>, CO folds, Button folds, <font color="#CC3333">Hero raises to $20</font>, UTG folds, MP3 calls $10.

Turn: ($60.50) T[img]/images/graemlins/club.gif[/img] <font color="#0000FF">(2 players)</font>
Hero checks, MP3 checks.

River: ($60.50) 8[img]/images/graemlins/club.gif[/img] <font color="#0000FF">(2 players)</font>
<font color="#CC3333">Hero bets $40</font>.....


In this hand, villian who bet the flop was a pretty tight VPIP player who seemed to play a very standard preflop game. I had been at this table for over 150 hands. I figured his hands he would call an EP raise with here were medium pocket pairs and higher, or high broadway cards. Assuming that, his bet on the flop made me 70% sure he was on an overpair. The c/r on the flop was for flush value and to take control of the hand, and for protection of my overcards.

After he checked behind on the turn, I figured he was scared of the 3 on the flop. I knew he had somewhat of a strong hand because he called my checkraise fairly quickly. My check on the turn also signaled that I was possibly scared of the 10.

So then comes the river, the 8. I figured this was the perfect card for me to bluff at. The way I played the hand signaled I could possibly be holding an 8. Of course so could he. But with the strength he played the flop and his PF tight standards, I felt that this was unlikely. So I jammed the river hard.

Thoughts? Was this a wreckless bet sure to get called? Or did I make decent reads good enough to know what he had?