I plan to prestretch a poly string, and a syn gut string. Is there a set amount of time I should pre-stretch each string? Also, I have noticed when I prestretched my Gosen Sheep 17 for about a minute heavily leaning (pulling) with my body weight. My racquet tends to feel a bit boardy when I do this. Should I lean less? lean for lesser amount of time? What are your suggestions for Poly? One last concern about poly. Someone mentioned that poly loses tension the fastest after its clamped off, is this true?