Nut Hand: What's the best play?

[D.J.]

20-40 blind game at commerce last night, the must move game was short until a guy who is a big donator sits down. I didn't intend on playing but saw the donator and hopped on the bus. I sit down w/ $5k, stacks range from $3-$30k. I had only been at the table for about 20 minutes and was up about $700. I'm 2nd to act and make it $160 to go w/ A [img]/images/graemlins/club.gif[/img]9 [img]/images/graemlins/club.gif[/img] 4 players call including the donator on the button who has around $20k. Flop comes:

K [img]/images/graemlins/club.gif[/img]8 [img]/images/graemlins/club.gif[/img]4 [img]/images/graemlins/club.gif[/img]

BB checks, I bet $240, everyone folds except donator who calls on the button. Turn 2 [img]/images/graemlins/heart.gif[/img], I bet $500, donator calls, River 6 [img]/images/graemlins/club.gif[/img], what's the best play?

-D.J.