Played this hand a while ago so I don't remember every detail of it.. please bear with me.

The table was fairly solid with a couple of rec players.  Villain (UTG+2) was someone I played against in a high-stakes buy-in MTT a long time ago.  My impression was that he was quite passive and limpy (he once limp/called 10bb with AQo when we were heads up), but I'm not sure how much of that would translate into cash game.

We both started the hand with about 200bb deep ($1k), and there was no short stack (<80bb) at the table.

I straddled UTG for $10 and get 5 callers or something.  I look down at Q6o and check.

Flop ($60) 664r 

I check, villain bets for $40 or so, everyone else folds and I call.  I didn't think I could get this in profitably for 200bb deep, when this passive guy bets into a 5-way pot.

Turn ($140) 664r 4

No more kicker problems.  I check, villain bets $80 and I call again.  I obv have a very good hand, but problem is, if I raise here I can rep very little air since I probably wouldn't even play 4x this way.  So the plan was to x/r on most rivers.

River ($300) 664r 4 K

I check and he quickly shoves for almost $900.

????????

On one hand, I'm just at the top top of my range.  On the other hand, I just can't see him bluffing (or value betting worse) in this spot like ever, and I wonder if he will shove with 6x always.  There aren't that many hands that beat me, namely K6, KK and 44.  KK is a bit unlikely but possible, K6 I'm not sure, 44 is def possible although that's just one combo.  

Snap call?  Tank call?  Is folding ever an option here?