I had one of my previous racquets strung at 70# with Prince Beast poly. It was really tough on my arm. I cut it out after two matches.
The mid to high 40s didn't really do a whole lot for me. However, I did see a significant difference when I started getting below 40#. When I got down to 30#, I saw a dramatic difference in performance.
Gotta run as I am off to try my natural gut setup in my league tonight.
Will report back later.
Evil doers ... you face The Tick!