Flop top set in a huge multi-way pot. When do I hit the brakes?

[paperboyNC]

I just sat down at the table and posted. Only read is the average pot is 8BB.

Party Poker 2/4 Hold'em (9 handed) converter

Preflop: Hero is MP2 with T[img]/images/graemlins/club.gif[/img], T[img]/images/graemlins/heart.gif[/img]. Hero posts a blind of $2.
UTG calls, UTG+1 calls, <font color="#666666">1 fold</font>, <font color="#CC3333">Hero (poster) raises</font>, <font color="#CC3333">MP3 3-bets</font>, <font color="#666666">4 folds</font>, UTG calls, UTG+1 calls, <font color="#CC3333">Hero caps</font>, MP3 calls, UTG calls, UTG+1 calls.

Flop: (17.50 SB) T[img]/images/graemlins/spade.gif[/img], 8[img]/images/graemlins/club.gif[/img], 5[img]/images/graemlins/spade.gif[/img] <font color="#0000FF">(4 players)</font>
UTG checks, <font color="#CC3333">UTG+1 bets</font>, <font color="#CC3333">Hero raises</font>, MP3 calls, UTG folds, <font color="#CC3333">UTG+1 3-bets</font>, <font color="#CC3333">Hero caps</font>, MP3 calls, UTG+1 calls.

Turn: (14.75 BB) A[img]/images/graemlins/spade.gif[/img] <font color="#0000FF">(3 players)</font>
UTG+1 checks, <font color="#CC3333">Hero bets</font>, <font color="#CC3333">MP3 raises</font>, UTG+1 calls, <font color="#CC3333">Hero 3-bets</font>, <font color="#CC3333">MP3 caps</font>, UTG+1 calls, Hero calls.

River: (26.75 BB) 9[img]/images/graemlins/club.gif[/img] <font color="#0000FF">(3 players)</font>
UTG+1 checks, <font color="#CC3333">Hero bets</font>, <font color="#CC3333">MP3 raises</font>, UTG+1 calls, Hero ?

<font color="#0000FF">What am I up against? </font>

- Does either player have the spade flush?
- Did the ace give MP3 a bigger set?
- The river seems to be a blank

<font color="#0000FF">Should I raise?</font>

The most I can lose by raising is 2BB. If I have the best hand I win 4BB. Am I beat more than a third of the time here?