Always better to err towards the stiff side than weak side. I shoot 300 spine arrows with my 65 lb bow and also with my 60 lb bow. They shoot right alongside my 400 spine arrows. I also shoot aluminum 2613 arrows that are almost like shooting rebar. (not sure of the spine, but I know it exceeds 300) They shoot extremely well. I was shooting them today with my 60 lb bow and was hitting a roofing nail at 10 yards. (started to zero in for hunting with that bow and arrow choice). Always with spine, you need to take into consideration the weight of the broad head. My guess would be that with the 500 spine arrow cut to 27 inches, you would have to use an 85 grain head or lighter so you are not under spined. I have a computer program that will tell you for sure, but right now I am at my laptop instead of my desk top where I have the program.