I have some hickory self bows that Ken 75 made, they are in mid 50# range and all are smaller than yours 52" to 56", draw easily to my 27+" draw and after 100's of arrows they are just gettin better. Yesterday I retillered a 55" NA Pyramid that he made because I couldn't pull it.....the weight was well above 70# and finally got it down to the low 60#'s.
Based on my experience, I dont think you are anywhere near the limits of Hickory.....JMO
rich