I have the pro-spec 757 S in a 580XD and I liked the shaft quite a bit. Very smooth feeling shaft and truly the first time I felt a shaft kick. My swing speed is 105-110 and the shaft is untipped, if I swing smooth i get great results but I cannot go after one with this set-up. I am thinking about buying an X and putting in the J33 460 9.5 driver.
It offers great flight, trajectory and distance, very consistant.