Oops! I missed where you'd mentioned draw length. I'll mention my POC setup and it might help. First off, I have 2 longbows - one is a high efficiency bow that is 74# @ 28" and the other is an extremely high efficiency bow that is 61# @ 28". My drqw length is righ at 28" and shooting the same arrow, the 2 bows fling any give arrow at virtually the same speed. What I'm finding that a POC shaft cut to 29" with a 190 grain field point flies very nicely from both of these bows. Finished weight comes in around 610-620 grains. I'm getting an arrow velocity around 165 fps.
EDIT: I forgot to mention that my shafts are spined at 85-90 (though I could also get away with 80-85s)