With everything else being equal, is it true add 5# spine for fast flight on POC?
I don't.
It can make a difference, but in my experience, more like 2 lbs. As with most things, I'm sure it makes more difference with some bows than others.
I don't know about poundage,all I did was to shorten my wood arrows about 3/4" to 1" when I swtiched to a FF type string over the dacron I had on it.
Yea it just depends on shooting style and how "close" you gotta be for good flight. I generally don't notice much more difference than extra strands or different silencers etc.