I always thought of it as cast that I picked up more so than poundage. You should get around 5- 10 lbs. Be careful to not go too heavy with it or you'll actually slow your bow down.
I really always thought of it as an insurance policy against breakage. It can also make you bow pull sweeter(IMHO) kinda like a huge rubber band with zip.
Good luck, its a fun project and sooooo much more fun to do than putting feathers on an arrow..lol
God bless,Mudd