4th Nut? Massive Overbet? Why the hell not!

[kagame]

So I've recently tried to shake things up in the $1000NL on Party. I have been getting called by the most ridiculous hands, its really incredible. Anyway, Villain seems to be a chronic slowplayer, and I'm praying he has a set and can call me. I'm beating a large number of flushes that also would call. How high is my risk factor here of running into a higher flush would you say? Is this a great overbet, silly for reasons of not getting value, or just plain moronic? Ready set go!

Party Poker No-Limit Hold'em, $6 BB (8 handed) converter

saw flop|<font color="#C00000">saw showdown</font>

<font color="#C00000">Hero ($761.4)</font>
UTG ($594)
UTG+1 ($970.92)
MP1 ($565.05)
MP2 ($641.85)
CO ($876.15)
<font color="#C00000">Button ($740.05)</font>
SB ($717.35)

Preflop: Hero is BB with J[img]/images/graemlins/spade.gif[/img], 7[img]/images/graemlins/spade.gif[/img].
<font color="#666666">1 fold</font>, <font color="#CC3333">UTG+1 raises to $18</font>, <font color="#666666">3 folds</font>, Button calls $18, <font color="#666666">1 fold</font>, Hero calls $12.

Flop: ($57) 3[img]/images/graemlins/spade.gif[/img], A[img]/images/graemlins/heart.gif[/img], 8[img]/images/graemlins/spade.gif[/img] <font color="#0000FF">(3 players)</font>
Hero checks, <font color="#CC3333">UTG+1 bets $45</font>, Button calls $45, Hero calls $45.

Turn: ($192) 6[img]/images/graemlins/spade.gif[/img] <font color="#0000FF">(3 players)</font>
Hero checks, UTG+1 checks, <font color="#CC3333">Button bets $75</font>, Hero calls $75, UTG+1 folds.

River: ($342) 7[img]/images/graemlins/heart.gif[/img] <font color="#0000FF">(2 players)</font>
<font color="#CC3333">Hero bets $623.4 (All-In)</font>

Final Pot: $1567.45