Octane requirement

I'm running a 300hp crate 360 magnum, it has 20 thousand miles on it right now, it has 9.0:1 compression ratio, I'm running 16 degrees of initial timing and 34 degrees total timing.
I live 4000 feet above sea level, I ran a compression test on it while warm with the carburetor wide open and it read 150 psi on every cylinder.
Based on that information am I safe to run regular 87 octane fuel in it? Or should I run 91 octane fuel in it? My timing is all in by 3000 rpm.
I can't hear any knock h running regular 87 but the exhaust is pretty loud so I'm not sure I would hear it if it was knocking.
What do you guys think?