[(psi used/working pressure) x cylinder capacity] / {[(depth/33)+1] x minutes}

If I go from an AL80 tank with a working pressure of 3000 to a steel HP80 with a working pressure of 3400 and everything else remaining the same, mathematically, my SAC rate goes down because of reducing the numerator based on the higher working pressure of the HP tank.

I'm not a Tech diver but this is instructive for me. SAC rate is not simply "What is your rate of consumption" but more importantly "How long will my gas last?" That's the question a Tech diver would ask, correct? I've always calculated simply my consumption rate and compared to the tank capacity.