I am using Klip Legend natural gut 18ga with Isospeed Professional17ga mains strung at 55/58. I really like the crisp feeling of the setup. All of a sudden the racket which has been a perfect stick for me feels different and does not play the same. I have about 15-20 sets on the string job. Have I gone to long on the Isospeed? I don't understand because I see players using Prince synthetic gut for over a year. Of course I don't know how their racket feels but mine does not have the same liveliness and pop to it. How often do I need to change the string? I am not a big hitter just a aggressive USTA 3.5 playing about 4 times a week.