Why don't you like the river card? I would like that river card very much. If you were ahead on the turn you are ahead now.
On this type of draw-heavy board almost nobody is slowplaying a set. Especially not with this many people in. And especially not because there are several players left to act after him. Besides, we can eliminate KK meaning the only two sets he can have are 99 and 44 (let's assume he didn't call the flop with 55). I would expect almost everyone to checkraise their set here.
When he smooth-calls you have to put him on one of two hands - either a weak King (KT-KQ), or a draw. When the flush card hits and he again calls your bet, I would no longer include a King in his range of hands - he's almost always on a flush now. When he bets $70 on that river, it's usually gonna be a bet that's asking for a call - I would fold without a read. What other hand could he have? Not many players call off big bets with gutshots, and looking at the action through the turn we can usually eliminate everything else by then.
And one other thing. I don't like to play
![The Six of Hearts [6h]](https://pofex.com/images/smilies/6h.gif)
[3h] in 5-way pots. The reason why is that even when you make your flush you are always gonna be afraid of a bigger flush such as in a case like this. Bottom two really isn't strong 5-way and could easily be beat by higher two pair or be counterfeited when the board pairs. Trips aren't that great because it lacks deception. The little straight is really the only thing that you can make and feel very good about your hand. I think this type of hand does play VERY well headsup or even 3-way though, especially if you are the preflop aggressor.