I probably shouldn't admit this, but it might help you so I will.
When I got my 53# Blacktail recurve I struggled finding the right spine. Everything that should have worked showed weak, from 65# on up.
In desperation, I talked to Snag and he sent me a half dozen of his own personal arrows spined at an average of 78#(that is one of the reasons why I am going to miss that guy and his arrows!). Anyway, I shot them and they worked.
The next year, I was practicing with some carbons- I was shooting a lot- getting ready for the fall. I remember I started moving out further, about twent-five yards, and I started shooting my 78# arrows with 180 grins up front. Thing was, I was seeing indications that the spine was too stiff. I could see it in the flight.
Back to the drawing board. I started shooting different spined arrows working back down. Believe it or not, when I went bear hunting last spring I was shooting 62/63# Sitka Spruce with 160 grn heads and they flew beautifully.
I am convinced when I was shooting heavier and heavier spined arrows I was just putting a band aid on poor technique/ form. I think I was torquing the bow.
I became much more consistent with the lighter spined arrows. So, I am sold on shooting and just watching the flight and impact of my arrows as Ken Beck suggested in his video on tuning.
Somebody here, I think Terry said form trumps all.