Spine by far is more important than FOC. I'll bet dollars to donuts that alot of top shooters have no idea what their FOC is. For confirmation on this, go check out Bob Ragsdales page. He says that his son (a top shooter) has never verified his FOC yet he's still winning tournaments.

Actually come to think of it, I haven't the faintest idea what MY FOC is. I honestly don't care either. My bow seems to shoot perfectly fine and group broadheads very well.

I've heard that a FOC somewhere between 9%-15% for hunting arrows is recommended however, there is no such thing as an established perfect FOC for each setup.

-Mike