Definitely go with the length on the sticker. I know one "pro shop" that would take the string off, put it on the jig and make the new string the same size. Doing this will make your bow different then what it was designed as.
Bow string material again is up to you. Check out
www.bcyfibers.com and they list break strengths, etc. Should help some in your research. As to shooting faster with a new string, chances are as the string stretches you will shoot faster because your draw length increases as the string stretches. That is why I use 450 Plus. It stays the same length I make it at.