$25NL KK, proper turn play with the overpair

[SumZero]

Ultimate Bet No-Limit Hold'em, $.25 BB (10 handed)

Villian is 15/5/2.1 based on ~375 hands

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

CO ($77.30)
Button ($10.70)
<font color="#C00000">Hero ($24.75)</font>
BB ($25)
UTG ($23.95)
UTG+1 ($8.25)
UTG+2 ($9.15)
<font color="#C00000">MP1 ($54.90)</font>
MP2 ($32)
MP3 ($31.85)

Preflop: Hero is SB with K[img]/images/graemlins/spade.gif[/img], K[img]/images/graemlins/diamond.gif[/img].
<font color="#666666">2 folds</font>, <font color="#CC3333">MP1 raises to $1</font>, <font color="#666666">4 folds</font>, <font color="#CC3333">Hero raises to $3.25</font>, <font color="#666666">1 fold</font>, MP1 calls $2.25.

Flop: ($6.75) 9[img]/images/graemlins/spade.gif[/img], 6[img]/images/graemlins/spade.gif[/img], Q[img]/images/graemlins/club.gif[/img] <font color="#0000FF">(2 players)</font>
<font color="#CC3333">Hero bets $4.25</font>, MP1 calls $4.25.

Turn: ($15.25) 4[img]/images/graemlins/diamond.gif[/img] <font color="#0000FF">(2 players)</font>

What's my best line?