Turned straight OOP

[Atropos]

Party Poker No-Limit Hold'em, $ Hero (6 max, 6 handed) FTR converter on zerodivide.cx

CO ($410.60)
Button ($387.20)
SB ($822.40)
Hero ($400)
UTG ($237.90)
MP ($977.90)

Preflop: Hero is BB with 6[img]/images/graemlins/club.gif[/img], 7[img]/images/graemlins/club.gif[/img]. SB posts a blind of $2.
[color=#666666]1 fold</font>, [color=#CC3333]MP raises to $8</font>, CO calls $8, [color=#666666]1 fold</font>, SB (poster) calls $6, Hero calls $4.

Flop: ($32) 4[img]/images/graemlins/spade.gif[/img], K[img]/images/graemlins/spade.gif[/img], 5[img]/images/graemlins/diamond.gif[/img] [color=#0000FF](4 players)</font>
SB checks, Hero checks, [color=#CC3333]MP bets $10</font>, CO calls $10, SB folds, Hero calls $10.

Turn: ($62) 8[img]/images/graemlins/diamond.gif[/img] [color=#0000FF](3 players)</font>
Hero checks, [color=#CC3333]MP bets $15</font>, CO calls $15, [color=#CC3333]Hero raises to $85</font>, MP folds, CO folds.

Final Pot: $177

Results in white below: [color=#FFFFFF]
No showdown. Hero wins $177. </font>

MP was very tight, thats why I hoped he had KK/set and would go broke [img]/images/graemlins/smile.gif[/img] CO seemed tight too, but called me down strangely on a hand earlier, caught me bluffing.
What shall I do on the turn? I could of course bet out, but how much? If I make a potsized bet against a good player it seems I'm losing money on this board, because around 50% of the time the river will make a flush possible, and then it's crazy hard for me if they push all-in.