Observed 25/50 Hand: What's Your Minimum to Stack off With?

[FoxwoodsFiend]

6-way pot limped preflop.
Flop (300): 3 [img]/images/graemlins/club.gif[/img] 4 [img]/images/graemlins/spade.gif[/img] 7 [img]/images/graemlins/club.gif[/img]
Checked to the tightest player at the table, who bets 200. The small blind requires some explanation. He's a donk, but he's not playing crazy. He's one of those guys who thinks that playing tight is enough to make him not that bad so he generally plays postflop without much of a clue other than "don't call it off with nothing." He's also clearly very wealthy. In sum, he's an old touristy guy who hasn't shown anything special.

Anyway, he check/raises to 900 and tight guy calls.

Turn (2100): 4 [img]/images/graemlins/club.gif[/img]
Please note in case you're not paying attention that this puts up a straight flush.
The old guy checks and the tight guy bets 1600, old guy calls.
River (5300): 7 [img]/images/graemlins/spade.gif[/img]
Old guy takes a stack of 20k and sets it to the side as he plays with another stack of cash with about 6k in it. He flips the stack over again and again and again and then sets it down and takes the 20k stack and puts it in the middle with authority but not overly strongly. It is 17k to the tight guy.

In this situation, if you're the tight guy, what do you call with?