Power Draw definitely increases accuracy. How it compares with WPF is unclear to me, but you can see a gif animation I made to compare bows here.
http://forum.c-rpg.net/index.php/topic,12057.0.htmlI used the same character, and simply switched bows. The bows with lower PD requirements are progressively and significantly more accurate, confirming that having PD above the requirement improves accuracy. My guess is that the base Accuracy Rating of the bow is altered proportionally by some value derived from the ratio of your PD versus the bow's required PD.
How then to create the most accurate archer possible? The jury's still out, since I don't understand yet how WPF affects accuracy. When I get to make another "skip the fun" character I'll do another test, at which time I'll also try to test whether rate of fire is affected by PD, but I'm fairly certain that that depends entirely on WPF. The other question to investigate is how long you can hold the crosshairs steady. The easier bows allowed for MUCH longer sustain, but this was also true of another archer character I made who only had PD 4 instead of 7. So I think the higher PD bows just don't maintain their aim as long, regardless of the character's PD. Still need to test. Hope this is helpful!
P.S. I have no idea why the Horn Bow was so out of place in this test, that's why I posted the animation in the Bug Forum.