There are some interesting points here, I have used both over an extended period of time, if you chronegraph both you will fine that the 54 will be quite a bit faster and flatter shooting than the 58 and that if you load it heavy enough to get over 2000 FPS it will generally drop a whitetail on the spot with a good heart lung hit [right on the back edge of the shoulder a couple inches behind the bone and 2 to 4 inchesabove the heart has done well for me of course if you dont hit them in the right place it wont make any differance what you are shooting; as for the 58 I eventually sold mine the 54 was so much flatter shooting and dropped them on the spot much more often, both of mine had the 1-66 twist and it work ok but the 58 ball was much heavier and the recoil and the twist controled how much you could get out of it, I have come to believe that for PRB the 54 is the best there is. Lee