I am 52 years old, 3.5 player on a good day, and I split my time between singles and doubles. I play 1-2 times per week and spend some time with my ball machine when I can't find a partner. I have a pretty strong serve and forehand, and am developing enough confidence in my 1HBH to swing all out during matches. When I allow myself to swing all out, my backhand actually produces better passing shots than the forehand but with a little less placement. I am not as comfortable at net and hit the frame a lot on volleys when I use anything under 100 square inches. I have played with a flock of Babolat tweeners for the past few years and finally realized that they have been the cause of my arm/shoulder discomfort. As a result, I am going to sell them off and purchase a Pro Kennex racquet. Here is where I need advice from the PK gurus on the forum. I am considering the PK Ki 15 260, Ki 15 PSE, Ki 20, and Ki 20 PSE. Beside the obvious weight and head size difference, what else differentiates these racquets? I will demo all of them before deciding, but would like to hear your personal experiences with each of them. Thank you so much in advance.