[Vinetou]

You are only taking about maximizing your equity against a draw. You are not taking into account other possible hands he might have and especially if he is a weak opponent, he might get stacked on. Those hans include two pair(don't have reads, but it is strange if he raised with Q9 or Q8 oop), overpair like kings or aces, AQ - I mean those hands without a draw to go with it. He might felt it on those hands. You are missing value from them if you let another card fall off. It might be a scare card or your line might convince him that you have even better hand that you have - a flopped flush.

Also, if he has a flush, you get your money in better (I mean less an underdog than if you wait until the turn).

What I am trying to say is that you are not taking into account other variables, just maximizing your equity against a flush draw.