[The Dude]

Let's do some very quick math here. Assuming the pfr is going to fold for two more AND the flop raiser is going to cap (this is worst-case scenario as far as pot odds goes), you'll be getting 19:4 to see a turn card (9.5:2 is a better way to look at it, since you're impied odds are in terms of big bets).

So if we ignore implied odds altogether, you need just under 10 outs in order to call. You have 4 outs 100% of the time, so your other 8 flush outs must be good roughly 75% of the time in order to call. (This is a bit over-simplified, but I think it's a good place to start.)

I'm not sure why everybody seems so convinced that there's a bigger flush draw out there. The flop raiser almost certainly doesn't have one, and while the 3-better could have a flush draw, I think it'd be more likely had he just cold-called. The original pfr could have a flush draw, but there's no reason to think he does either.

I really can't see folding being the best play. Nothing about the way the action's gone down so far screams flush draw to me. I think you're more likely to be up against a set than a flush draw.

Cap it up. You've got pretty good equity in this hand, and capping it keeps your hand disguised.