Well I have gone for the build of 24 Str, 15 Agi, 8PD, 5 IF, 5 Athletics, 5WM, 8 converted skill points. This yeilds a WPP of 147 without any points placed in any other weapon proficiency. From my understanding once you reach 145+ WPP in archery PD becomes more efficient for reducing crosshair size, aswel as damage of course, however you do no gain draw speed with PD. Hope this helps, still not got the 8 PD I will get it at level 30 but up to now the crosshair is looking nice. The bow became predictably accurate around 125 WPP for me, but was not perfect for anything but close range.