Blind vs blind against an unknown - turned flush [betsizing]

[thac]

Full Tilt Poker - No Limit Hold'em Cash Game - $1/$2 Blinds - 6 Players - (LegoPoker HH Converter)

SB: $210.20
Hero (BB): $203.00
UTG: $219.70
MP: $90.30
CO: $248.60
BTN: $196.55

Preflop: Hero is dealt 9[img]/images/graemlins/diamond.gif[/img] 4[img]/images/graemlins/diamond.gif[/img] (6 Players)
4 folds, SB calls $1.00, Hero checks

Flop: ($4) 8[img]/images/graemlins/diamond.gif[/img] 5[img]/images/graemlins/diamond.gif[/img] 7[img]/images/graemlins/heart.gif[/img] (2 Players)
<font color="red">SB bets $2.00</font>, Hero calls $2.00

Turn: ($8) T[img]/images/graemlins/diamond.gif[/img] (2 Players)
<font color="red">SB bets $4.00</font>, <font color="red">Hero raises to ???</font>


What do we raise to here in a vacuum? Player just sat and posted the BB one hand ago and won a pot. Alternate lines work too (raising flop or something goofy)