It has been proven that wpf increases accuracy, and PD merely makes the reticule "hold" longer at the optimum position, as well as increasing damage at all ranges. Also from what I can see, among other archers as well, PD no longer makes your bow less accurate.
As for the longbow, I had success with it at 130 wpf for a "shotgun" against cavalry, though for long distance shooting I would try and go for at least 150 with it.
XBows have recently been concretely proven that the base accuracy (I think walt did it) does not effect your shot at all, and regardless of your wpf the reticule will be identical whether you are using a light xbow or a sniper or any of the others.
I have yet to see a similar test for bows (hopefully walt will do this), though I think the base accuracy for them actually matters.
I am tempted to just buy the last few bows I do not own, and make my own experiments with them to test the "accuracy" effect, just timing the screenshots to match the reticul at the best position would be an utter pain (unlike the xbows).