i don't know what it is about guts, but even with professional stringing i tend to break it at the 8 hour mark. i have yet to break any poly, but they tend to drop in tension pretty quickly. i usually string 3 pounds higher and let it sit for a day before i use it and the tension stability is perfect for me.
my only complaint is i don't 100% like how the racquet is balanced. over the past 2 years i've been messing around with the weight but i can't find the balance i like without sacrificing plowthrough and control.
exo3 tour with cyclone main/co focus crosses at 54/56 pounds