If you shoot 61-64lbs you will reap more benefits of the #50-60's. I picked up as much as 6-8fps on a 50-60 maxed at 63 compared to a 60-70 at 63. exact same DL, and setup.
What kind of bow?
What I like about the 60-70 @ 63#'s is, though......I can go to 70#'s if I want.