I am a 5.0 player, and I string my own rackets (RDX300 @ 61lbs). I do this mainly because I hit hard and with a lot of spin, and I end up popping strings, on average, ever 3-4 hrs of play.
I used to break every 2hrs when I was using a 16 gage string.
Now I use a hybrid of 15g Prince Nylon...